Pharmasset, Inc. Common Stock UNDERWRITING AGREEMENT dated April 25, 2007 Banc of America Securities LLC UBS Securities LLC

EXHIBIT 1.1

Pharmasset, Inc.

Common Stock

UNDERWRITING AGREEMENT

dated April 25, ▇▇▇▇

▇▇▇▇ ▇▇ ▇▇▇▇▇▇▇ Securities LLC

UBS Securities LLC

Underwriting Agreement

April 25, ▇▇▇▇

▇▇▇▇ ▇▇ ▇▇▇▇▇▇▇ SECURITIES LLC

▇ ▇▇▇▇ ▇▇^▇▇ ▇▇▇▇▇▇

▇▇▇ ▇▇▇▇ , ▇▇ ▇▇▇▇▇

UBS SECURITIES LLC

▇▇▇ ▇▇▇▇ ▇▇▇▇▇▇

▇▇▇ ▇▇▇▇, ▇▇ ▇▇▇▇▇

As Representatives of the several Underwriters named in Scheduled A hereto

Ladies and Gentlemen:

Introductory. Pharmasset, Inc. a Delaware corporation (the “Company”), proposes to issue and sell to the several underwriters named in Schedule A hereto (the “Underwriters”) an aggregate of [ ] shares (the “Firm Shares”) of its Common Stock, par value $0.001 per share (the “Common Stock”). In addition, the Company has granted to the Underwriters an option to purchase up to an additional [ ] shares (the “Optional Shares”) of Common Stock, as provided in Section 2. The Firm Shares and, if and to the extent such option is exercised, the Optional Shares are collectively called the “Shares”. Banc of America Securities LLC (“BAS”) and UBS Securities LLC (“UBS”), the joint book-running managers in connection with the offering, have agreed to act as representatives of the several Underwriters (in such capacity, each, a “Representative” and collectively, the “Representatives”) in connection with the offering and sale of the Shares.

The Company hereby confirms its agreements with the Underwriters as follows:

SECTION 1. Representations and Warranties of the Company.

The Company hereby represents and warrants to, and covenants with each Underwriter, as of the date of this Agreement and as of each Closing Date and any Subsequent Closing Date, as follows:

(a) The Company has prepared and filed with the Securities and Exchange Commission (the “Commission”) a registration statement on Form S-1 (File No. 333-133907), which contains a form of prospectus to be used in connection with the public offering and sale of the Shares.

Such registration statement, as amended, including the financial statements, exhibits and schedules thereto, in the form in which it was declared effective by the Commission under the Securities Act of 1933, as amended, and the rules and regulations promulgated thereunder (collectively, the “Securities Act”), including any required information deemed to be a part thereof at the time of effectiveness pursuant to Rule 430A under the Securities Act, is called the “Registration Statement”. Any registration statement filed by the Company pursuant to Rule 462(b) under the Securities Act is called the “Rule 462(b) Registration Statement”, and from and after the date and time of filing of the Rule 462(b) Registration Statement the term “Registration Statement” shall include the Rule 462(b) Registration Statement. Any preliminary prospectus included in the Registration Statement is hereinafter called a “preliminary prospectus.” The term “Prospectus” shall mean the final prospectus relating to the Shares that is first filed pursuant to Rule 424(b) after the date and time that this Agreement is executed and delivered by the parties hereto (the “Execution Time”) or, if no filing pursuant to Rule 424(b) is required, shall mean the form of final prospectus relating to the Shares included in the Registration Statement at the effective date. All references in this Agreement to the Registration Statement, the Rule 462(b) Registration Statement, a preliminary prospectus, the Prospectus, or any amendments or supplements to any of the foregoing, shall refer to the version thereof filed with the Commission pursuant to its Electronic Data Gathering, Analysis and Retrieval System (“▇▇▇▇▇”).

(b) Compliance with Registration Requirements. The Registration Statement has been declared effective by the Commission under the Securities Act. No stop order suspending the effectiveness of the Registration Statement is in effect and no proceedings for such purpose have been instituted or are pending or, to the best knowledge of the Company, are contemplated or threatened by the Commission.

The preliminary prospectus included in the General Disclosure Package (as defined below) and the Prospectus when filed pursuant to Rule 424(b) complied in all material respects with the Securities Act. Each of the Registration Statement and any post-effective amendment thereto, at the time it became effective and at the date hereof, complied and will comply in all material respects with the Securities Act and did not and will not contain any untrue statement of a material fact or omit to state a material fact required to be stated therein or necessary in order to make the statements therein not misleading. The Prospectus, as amended or supplemented, as of its date, at the date hereof, at the time of any filing pursuant to Rule 424(b), at the Closing Date (as defined herein) and at any Subsequent Closing Date (as defined herein), did not and will not contain any untrue statement of a material fact or omit to state a material fact necessary in order to make the statements therein, in the light of the circumstances under which they were made, not misleading. The representations and warranties set forth in the two immediately preceding sentences do not apply to statements in or omissions from the Registration Statement or any post-effective amendment thereto, or the Prospectus, or any amendments or supplements thereto, made in reliance upon and in conformity with information relating to any Underwriter furnished to the Company in writing by the Representatives expressly for use therein, it being understood and agreed that the only such information furnished by the Representatives consists of the information described as such in Section 8 hereof. There is no contract or other document required to be described in the Prospectus or to be filed as an exhibit to the Registration Statement that has not been described or filed as required.

(c) Disclosure Package. The term “Disclosure Package” shall mean, collectively, (i) the preliminary prospectus, if any, as amended or supplemented as of the Applicable Time (as defined below), (ii) the issuer free writing prospectuses as defined in Rule 433 of the Securities Act (each, an “Issuer Free Writing Prospectus”), if any, identified in Schedule B hereto, (iii) any other free writing prospectus that the parties hereto shall hereafter expressly agree in writing to treat as part of the Disclosure Package and (iv) the information set forth on Schedule C hereto, indicating the number of Shares being sold and the price at which the Shares will be sold to the public. As of [__][a./p.]m. (Eastern time) on the date of this Agreement (the “Applicable Time”), the Disclosure Package does not contain any untrue statement of a material fact or omit to state any material fact necessary in order to make the statements therein, in the light of the circumstances under which they were made, not misleading. The preceding sentence does not apply to statements in or omissions from the Disclosure Package based upon and in conformity with written information furnished to the Company by any Underwriter through the Representatives specifically for use therein, it being understood and agreed that the only such information furnished by or on behalf of any Underwriter consists of the information described as such in Section 8 hereof.

(d) Issuer Free Writing Prospectuses. Each Issuer Free Writing Prospectus, as of its issue date, did not include any information that conflicted with the information contained in the Registration Statement. If at any time following issuance of an Issuer Free Writing Prospectus there occurred or occurs an event or development as a result of which such Issuer Free Writing Prospectus conflicted or would conflict with the information contained in the Registration Statement, the Company has promptly notified or will promptly notify the Representatives and has promptly amended or supplemented or will promptly amend or supplement, at its own expense, such Issuer Free Writing Prospectus to eliminate or correct such conflict. The foregoing two sentences do not apply to statements in or omissions from any Issuer Free Writing Prospectus based upon and in conformity with written information furnished to the Company by any Underwriter through the Representatives specifically for use therein, it being understood and agreed that the only such information furnished by any Underwriter consists of the information described as such in Section 8 hereof.

(e) Distribution of Offering Material by the Company. The Company has not distributed and will not distribute, prior to the later of the last Subsequent Closing Date (as defined below) and the completion of the Underwriters’ distribution of the Shares (of which the Underwriters will notify the Company), any offering material in connection with the offering and sale of the Shares other than the preliminary prospectus included in the Disclosure Package, the Prospectus, any Issuer Free Writing Prospectus reviewed and consented to by the Representatives or included in Schedule B hereto or the Registration Statement.

(f) The Underwriting Agreement. This Agreement has been duly authorized, executed and delivered by the Company.

(g) Authorization of the Shares. The Shares to be purchased by the Underwriters from the Company have been duly authorized for issuance and sale pursuant to this Agreement and, when issued and delivered by the Company to the Underwriters pursuant to this Agreement on the Closing Date or any Subsequent Closing Date, will be validly issued, fully paid and nonassessable.

(h) No Transfer Taxes. There are no transfer taxes or other similar fees or charges under federal law or the laws of any state, or any political subdivision thereof, required to be paid in connection with the execution and delivery of this Agreement or the issuance by the Company or sale by the Company of the Shares.

(i) No Applicable Registration or Other Similar Rights. There are no persons with registration or other similar rights to have any equity or debt securities registered for sale under the Registration Statement or included in the offering contemplated by this Agreement, except for such rights as have been duly waived.

(j) No Material Adverse Change. Except as otherwise disclosed in the Disclosure Package and the Prospectus, subsequent to the respective dates as of which information is given in the Disclosure Package: (i) there has been no material adverse change, or any development that could reasonably be expected to result in a material adverse change, in the condition, financial or otherwise, or in the earnings, business, properties, operations or prospects, whether or not arising from transactions in the ordinary course of business of the Company (any such change is called a “Material Adverse Change”); (ii) the Company has not incurred any material liability or obligation, indirect, direct or contingent, nor entered into any material transaction or agreement; and (iii) there has been no dividend or distribution of any kind declared, paid or made by the Company on any class of capital stock or repurchase or redemption by the Company of any class of capital stock.

(k) Independent Accountants. ▇▇▇▇▇ ▇▇▇▇▇▇▇▇ LLP (“▇▇▇▇▇ ▇▇▇▇▇▇▇▇”), who have expressed their opinion with respect to the financial statements (which term as used in this Agreement includes the related notes thereto) and supporting schedules, if any, filed with the Commission as a part of the Registration Statement and included in the Disclosure Package and the Prospectus, are independent public accountants with respect to the Company as required by the Securities Act and the Securities Exchange Act of 1934, as amended (the “Exchange Act”) and the applicable rules and regulations thereunder.

(l) Preparation of the Financial Statements. The financial statements filed with the Commission as a part of the Registration Statement and included in the Disclosure Package and the Prospectus present fairly in all material respects the consolidated financial position of the Company as of and at the dates indicated and the results of its operations and cash flows for the periods specified on the basis stated therein. Such financial statements comply as to form with the applicable accounting requirements of the Securities Act and have been prepared in conformity with generally accepted accounting principles applied on a consistent basis throughout the periods involved, except as may be expressly stated in the related notes thereto. No other financial statements or supporting schedules are required to be included in the Registration Statement. The financial data set forth in the preliminary prospectus included in each of the Disclosure Package and the Prospectus under the captions “Summary—Summary Selected Consolidated Financial Data”, “Selected Consolidated Financial Data” and “Capitalization” fairly summarize in all material respects the information set forth therein on a basis consistent with that of the audited financial statements contained in the Registration Statement.

(m) Incorporation and Good Standing of the Company. The Company has been duly incorporated and is validly existing as a corporation in good standing under the laws of the jurisdiction of its incorporation and has corporate power and authority to own or lease, as the

case may be, and operate its properties and to conduct its business as described in the Disclosure Package and the Prospectus and, in the case of the Company, to enter into and perform its obligations under this Agreement. The Company is duly qualified as a foreign corporation to transact business and is in good standing in each jurisdiction in which such qualification is required, whether by reason of the ownership or leasing of property or the conduct of business, except for such jurisdictions where the failure to so qualify or to be in good standing would not, individually or in the aggregate, result in a material adverse effect, on the condition, financial or otherwise, or on the earnings, business, properties, operations or prospects, whether or not arising from transactions in the ordinary course of business of the Company (a “Material Adverse Effect”).

(n) Capitalization and Other Capital Stock Matters. The authorized, issued and outstanding capital stock of the Company is as set forth in each of the Disclosure Package and the Prospectus under the caption “Capitalization” (other than for subsequent issuances, if any, pursuant to employee benefit plans described in the Disclosure Package and the Prospectus, upon exercise of outstanding options or warrants described in the Disclosure Package and the Prospectus, or upon conversion of outstanding preferred stock described in the Disclosure Package and the Prospectus, as the case may be). The Common Stock (including the Shares) conforms in all material respects to the description thereof contained in each of the Disclosure Package and the Prospectus. All of the issued and outstanding shares of Common Stock have been duly authorized and validly issued, are fully paid and nonassessable and have been issued in compliance with federal and state securities laws. None of the outstanding shares of Common Stock were issued in violation of any preemptive rights, rights of first refusal or other similar rights to subscribe for or purchase securities of the Company. There are no Company authorized or outstanding options, warrants, preemptive rights, rights of first refusal or other rights to purchase, or equity or debt securities convertible into or exchangeable or exercisable for, any capital stock of the Company other than those described in the Disclosure Package and the Prospectus. The description of the Company’s stock option, stock bonus and other stock plans or arrangements, and the options or other rights granted thereunder, set forth in each of the Disclosure Package and the Prospectus accurately and fairly presents in all material respects the information required to be shown with respect to such plans, arrangements, options and rights.

(o) Quotation. The Shares have been approved for quotation on The Nasdaq Global Market, subject only to official notice of issuance.

(p) Non-Contravention of Existing Instruments; No Further Authorizations or Approvals Required. The Company is not (i) in violation or in default (or, with the giving of notice or lapse of time, would be in default) (“Default”) under its certificate of incorporation or by-laws, (ii) in Default under any indenture, mortgage, loan or credit agreement, deed of trust, note, contract, franchise, lease or other agreement, obligation, condition, covenant or instrument to which the Company is a party or by which it may be bound, or to which any of the property or assets of the Company is subject (each, an “Existing Instrument”), or (iii) in violation of any statute, law, rule, regulation, judgment, order or decree of any court, regulatory body, administrative agency, governmental body, arbitrator or other authority having jurisdiction over the Company or any of its properties, as applicable, except with respect to clause (ii) and (iii) only, for such Defaults as would not, individually or in the aggregate, have a Material Adverse Effect. The Company’s execution, delivery and performance of this Agreement and consummation of the transactions contemplated hereby, by the Disclosure Package and by the Prospectus (i) have been duly

authorized by all necessary corporate action and will not result in any Default under the charter or by-laws of the Company, (ii) will not conflict with or constitute a breach of, or Default under, or result in the creation or imposition of any lien, charge or encumbrance upon any property or assets of the Company pursuant to, or require the consent of any other party to, any Existing Instrument, and (iii) will not result in any violation of any statute, law, rule, regulation, judgment, order or decree applicable to the Company of any court, regulatory body, administrative agency, governmental body, arbitrator or other authority having jurisdiction over the Company or any of its or their properties. No consent, approval, authorization or other order of, or registration or filing with, any court or other governmental or regulatory authority or agency is required for the Company’s execution, delivery and performance of this Agreement and consummation of the transactions contemplated hereby, by the Disclosure Package and by the Prospectus, except such as have been obtained or made by the Company and are in full force and effect under the Securities Act, applicable state securities or blue sky laws and from the NASD Inc. (the “NASD”).

(q) No Material Actions or Proceedings. There are no legal or governmental actions, suits or proceedings pending or, to the best of the Company’s knowledge, threatened (i) against or affecting the Company, (ii) which has as the subject thereof any officer or director of, or property owned or leased by, the Company or (iii) relating to environmental or discrimination matters, where in any such case, if resolved adversely to the Company, would, individually or in the aggregate, have a Material Adverse Effect or adversely affect the consummation of the transactions contemplated by this Agreement.

(r) Labor Matters. No labor dispute with the employees of the Company exists or, to the Company’s knowledge, is threatened or imminent, and the Company is not aware of any existing or imminent labor dispute with the employees of any of its principal suppliers that could have a Material Adverse Effect.

(s) Intellectual Property Rights. Except as described in the Disclosure Package and the Prospectus, the Company owns, possesses, licenses or has other rights to use, on reasonable terms, all patents, patent applications, trade and service marks, trade and service ▇▇▇▇ registrations, trade names, copyrights, licenses, inventions, trade secrets, technology, know-how and other intellectual property (collectively, the “Intellectual Property”) that are necessary for the conduct of the Company’s business as now conducted or, in connection with its major product candidates, as proposed in each of the Disclosure Package and the Prospectus to be conducted. Except as set forth in the Disclosure Package and the Prospectus, (a) to the Company’s knowledge, there is no material infringement by third parties of any such Intellectual Property owned by or exclusively licensed to the Company; (b) there is no pending or, to the Company’s knowledge, threatened action, suit, proceeding or claim by others challenging the Company’s rights in or to any material Intellectual Property; (c) there is no pending or, to the Company’s knowledge, threatened action, suit, proceeding or claim by others challenging the validity or scope of any such material Intellectual Property; (d) to the Company’s knowledge there is no pending or, threatened action, suit, proceeding or claim by others that the Company’s business as now conducted infringes or otherwise violates any patent, trademark, copyright, trade secret or other proprietary rights of others; (e) to the Company’s knowledge the Company has complied in all material respects with the terms of each agreement pursuant to which material Intellectual Property has been licensed to the Company, and all such agreements are in full force and effect;

and (f) to the Company’s knowledge, the product candidates described in the Disclosure Package and the Prospectus, if any, as under development by the Company fall within the scope of the claims of one or more patents or patent applications owned by, or exclusively licensed to, the Company, and nothing has come to the Company’s attention that causes it to believe that such patents are not valid or enforceable.

(t) All Necessary Permits, etc. The Company possesses such valid and current licenses, certificates, authorizations or permits issued by the appropriate state, federal or foreign regulatory agencies or bodies necessary to conduct its business which, singly or in the aggregate, if not obtained, would have a Material Adverse Effect, and the Company has not received any notice of proceedings relating to the revocation or modification of, or non-compliance with, any such license, certificate, authorization or permit which, singly or in the aggregate, if the subject of an unfavorable decision, ruling or finding, could have a Material Adverse Effect.

(u) Title to Properties. The Company has good and marketable title to all the properties and assets reflected as owned in the financial statements referred to in Section 1(n) above, in each case free and clear of any security interests, mortgages, liens, encumbrances, equities, claims and other defects, except such as do not materially and adversely affect the value of such property and do not materially interfere with the use made or proposed to be made of such property by the Company. The real property, improvements, equipment and personal property held under lease by the Company are held under valid and enforceable leases, with such exceptions as are not material and do not materially interfere with the use made or proposed to be made of such real property, improvements, equipment or personal property by the Company.

(v) Tax Law Compliance. The Company has filed all necessary federal, state, local and foreign income and franchise tax returns in a timely manner and has paid all taxes required to be paid by it and, if due and payable, any related or similar assessment, fine or penalty levied against it, except for any taxes, assessments, fines or penalties as may be being contested in good faith and by appropriate proceedings. The Company has made appropriate provisions in the applicable financial statements referred to in Section 1(n) above in respect of all federal, state, local and foreign income and franchise taxes for all current or prior periods as to which the tax liability of the Company has not been finally determined.

(w) Company Not an “Investment Company”. The Company is not required to be registered as an “investment company” within the meaning of the Investment Company Act of 1940, as amended (the “Investment Company Act”).

(x) Insurance. Except as described in the Disclosure Package and the Prospectus, the Company is insured with policies in such amounts and with such deductibles and covering such risks as are generally deemed adequate and customary for its business. All policies of insurance insuring the Company or its businesses, assets, employees, officers and directors are in full force and effect; and there are no claims by the Company under any such policy or instrument as to which any insurance company is denying liability or defending under a reservation of rights clause.

(y) No Price Stabilization or Manipulation. The Company has not taken and will not take, directly or indirectly, any action designed to or that might be reasonably expected to cause or result in stabilization or manipulation of the price of any security of the Company to facilitate the sale or resale of the Shares. The Company acknowledges that the Underwriters may engage in stabilization transactions in accordance with Regulation M.

(z) Internal Controls and Procedures. The Company maintains a system of internal accounting controls sufficient to provide reasonable assurance that (A) transactions are executed in accordance with management’s general or specific authorizations; (B) transactions are recorded as necessary to permit preparation of financial statements in conformity with generally accepted accounting principles and to maintain asset accountability; (C) access to assets is permitted only in accordance with management’s general or specific authorization; and (D) the recorded accountability for assets is compared with the existing assets at reasonable intervals and appropriate action is taken with respect to any differences.

(aa) No Material Weakness in Internal Controls. Except as disclosed in the Disclosure Package and the Prospectus, since the end of the Company’s most recent audited fiscal year, (i) the auditors have not brought to the Company’s attention any material weakness in the Company’s internal control over financial reporting (whether or not remediated) and (ii) to the Company’s knowledge, there has been no change in the Company’s internal control over financial reporting that has materially affected, or is reasonably likely to materially affect, the Company’s internal control over financial reporting.

(bb) No Unlawful Contributions or Other Payments. Neither the Company nor, to the knowledge of the Company, any director, officer, or employee of the Company is aware of or has taken any action, directly or indirectly, that would result in a violation by such persons of the Foreign Corrupt Practices Act of 1977, as amended, and the rules and regulations thereunder (the “FCPA”), including, without limitation, making use of the mails or any means or instrumentality of interstate commerce corruptly in furtherance of an offer, payment, promise to pay or authorization of the payment of any money, or other property, gift, promise to give, or authorization of the giving of anything of value to any “foreign official” (as such term is defined in the FCPA) or any foreign political party or official thereof or any candidate for foreign political office, in contravention of the FCPA, and the Company has conducted its business in compliance with the FCPA.

(cc) Compliance with Environmental Laws. Except as otherwise disclosed in the Disclosure Package and the Prospectus, (i) the Company is not in violation of any federal, state, local or foreign law, regulation, order, permit or other requirement relating to pollution or protection of human health or the environment (including, without limitation, ambient air, surface water, groundwater, land surface or subsurface strata) or wildlife, including without limitation, laws and regulations relating to emissions, discharges, releases or threatened releases of chemicals, pollutants, contaminants, wastes, toxic substances, hazardous substances, petroleum and petroleum products (collectively, “Materials of Environmental Concern”), or otherwise relating to the manufacture, processing, distribution, use, treatment, storage, disposal, transport or handling of Materials of Environment Concern (collectively, “Environmental Laws”), which violation includes, but is not limited to, noncompliance with any permits or other governmental authorizations required for the operation of the business of the Company under applicable Environmental Laws, or noncompliance with the terms and conditions thereof, nor has

the Company received any written communication, whether from a governmental authority, citizens group, employee or otherwise, that alleges that the Company is in violation of any Environmental Laws, except as would not, individually or in the aggregate, have a Material Adverse Effect; (ii) there is no claim, action or cause of action filed with a court or governmental authority, no investigation with respect to which the Company has received written notice, and no written notice by any person or entity alleging potential liability for investigatory costs, cleanup costs, governmental responses costs, natural resources damages, property damages, personal injuries, attorneys’ fees or penalties arising out of, based on or resulting from the presence, or release into the environment, of any Material of Environmental Concern at any location owned, leased or operated by the Company, now or in the past (collectively, “Environmental Claims”), pending or, to the Company’s knowledge, threatened against the Company or any person or entity whose liability for any Environmental Claim the Company has retained or assumed either contractually or by operation of law, except as would not, individually or in the aggregate, have a Material Adverse Effect; (iii) to the Company’s knowledge, there are no past or present actions, activities, conditions, events or incidents, including, without limitation, the release, emission, discharge, presence or disposal of any Material of Environmental Concern, that reasonably could result in a violation of any Environmental Laws, require expenditures to be incurred pursuant to Environmental Laws, or form the basis of a potential Environmental Claim against the Company or against any person or entity whose liability for any Environmental Claim the Company has retained or assumed either contractually or by operation of law, except as would not, individually or in the aggregate, have a Material Adverse Effect; and (iv) the Company is not subject to any pending or, to the Company’s knowledge, threatened proceeding under Environmental Law to which a governmental authority is a party and which is reasonably likely to result in monetary sanctions of $100,000 or more.

(dd) ERISA Compliance. None of the following events has occurred or exists: (i) a failure to fulfill the obligations, if any, under the minimum funding standards of ▇▇▇▇▇▇▇ ▇▇▇ ▇▇ ▇▇▇ ▇▇▇▇▇▇ ▇▇▇▇▇▇ Employee Retirement Income Security Act of 1974, as amended (“ERISA”), and the regulations and published interpretations thereunder with respect to a Plan, determined without regard to any waiver of such obligations or extension of any amortization period; (ii) an audit or investigation by the Internal Revenue Service, the U.S. Department of Labor, the Pension Benefit Guaranty Corporation or any other federal or state governmental agency or any foreign regulatory agency with respect to the employment or compensation of employees by any member of the Company that could have a Material Adverse Effect; (iii) any breach of any contractual obligation, or any violation of law or applicable qualification standards, with respect to the employment or compensation of employees by any member of the Company that could have a Material Adverse Effect. None of the following events has occurred or is reasonably likely to occur: (i) a material increase in the aggregate amount of contributions required to be made to all Plans in the current fiscal year of the Company compared to the amount of such contributions made in the Company’s most recently completed fiscal year; (ii) a material increase in the Company’s “accumulated post-retirement benefit obligations” (within the meaning of Statement of Financial Accounting Standards 106) compared to the amount of such obligations in the Company’s most recently completed fiscal year; (iii) any event or condition giving rise to a liability under Title IV of ERISA that could have a Material Adverse Effect; or (iv) the filing of a claim by one or more employees or former employees of the Company related to their employment that could have a Material Adverse Effect. For purposes of this paragraph, the term “Plan” means a plan (within the meaning of Section 3(3) of ERISA) subject to Title IV of ERISA with respect to which any member of the Company may have any liability.

(ee) Brokers. Except as otherwise disclosed in the Disclosure Package and the Prospectus, there is no broker, finder or other party that is entitled to receive from the Company any brokerage or finder’s fee or other fee or commission as a result of any transactions contemplated by this Agreement.

(ff) No Outstanding Loans or Other Indebtedness. There are no outstanding loans, advances (except normal advances for business expenses in the ordinary course of business) or guarantees or indebtedness by the Company to or for the benefit of any of the officers or directors of the Company, except as disclosed in the Disclosure Package and the Prospectus.

(gg) Sarbanes Oxley Compliance. There is and has been no material failure on the part of the Company and, to the knowledge of the Company, any of the Company’s directors or officers, in their capacities as such, to comply with any provision of the Sarbanes Oxley Act of 2002 and the rules and regulations promulgated in connection therewith (the “Sarbanes Oxley Act”) that are applicable to the Company.

(hh) Subsidiaries. The Company has no subsidiaries.

(ii) Lending Relationship. Except as disclosed in the Disclosure Package and the Prospectus, the Company (i) does not have any material lending relationship with any bank or lending affiliate of any Underwriter and (ii) does not intend to use any of the proceeds from the sale of the Common Shares hereunder to repay any outstanding debt owed to any affiliate of any Underwriter.

Any certificate signed by an officer of the Company and delivered to the Representatives or to counsel for the Underwriters shall be deemed to be a representation and warranty by the Company to each Underwriter as to the matters set forth therein.

The Company acknowledges that the Underwriters and, for purposes of opinion to be delivered pursuant to Section 5 hereof, counsel to the Company and counsel to the Underwriters, will rely upon the accuracy and truthfulness of the foregoing representations and hereby consents to such reliance.

SECTION 2. Purchase, Sale and Delivery of the Shares.

(a) The Firm Shares. The Company agrees to issue and sell to the several Underwriters the Firm Shares upon the terms herein set forth. On the basis of the representations, warranties and agreements herein contained, and upon the terms but subject to the conditions herein set forth, the Underwriters agree, severally and not jointly, to purchase from the Company the respective number of Firm Shares set forth opposite their names on Schedule A. The purchase price per Firm Common Share to be paid by the several Underwriters to the Company shall be $[ ] per share.

(b) The Closing Date. Delivery of certificates for the Firm Shares to be purchased by the Underwriters and payment therefor shall be made at the offices of ▇▇▇▇▇ ▇▇▇▇ & ▇▇▇▇▇▇▇▇, ▇▇▇ ▇▇▇▇▇▇▇▇▇ ▇▇▇▇▇▇, ▇▇▇ ▇▇▇▇, ▇▇▇ ▇▇▇▇ ▇▇▇▇▇ (or such other place as may be agreed to by the Company and the Representatives) at 9:00 a.m. New York time, on April 30, 2007, or such other time and date not later than, 2007, as the Representatives shall designate by notice to the Company (the time and date of such closing are called the “Closing Date”).

(c) The Optional Shares; the Subsequent Closing Date. In addition, on the basis of the representations, warranties and agreements herein contained, and upon the terms but subject to the conditions herein set forth, the Company hereby grants an option to the several Underwriters to purchase, severally and not jointly, up to an aggregate of [ ] Optional Shares from the Company at the purchase price per share to be paid by the Underwriters for the Firm Shares. The option granted hereunder is for use by the Underwriters solely in covering any over-allotments in connection with the sale and distribution of the Firm Shares, and may be exercised at any time and from time to time upon notice by the Representatives to the Company, which notice may be given at any time within 30 days from the date of this Agreement. Such notice shall set forth (i) the aggregate number of Optional Shares as to which the Underwriters are exercising the option, (ii) the names and denominations in which the certificates for the Optional Shares are to be registered and (iii) the time, date and place at which such certificates will be delivered (which time and date may be simultaneous with, but not earlier than, the Closing Date; and in such case the term “Closing Date” shall refer to the time and date of delivery of certificates for the Firm Shares and the Optional Shares). Each time and date of delivery, if subsequent to the Closing Date, is called a “Subsequent Closing Date” and shall be determined by the Representatives and shall not be earlier than three nor later than five full business days after delivery of such notice of exercise. If any Optional Shares are to be purchased, each Underwriter agrees, severally and not jointly, to purchase the number of Optional Shares (subject to such adjustments to eliminate fractional shares as the Representatives may determine) that bears the same proportion to the total number of Optional Shares to be purchased as the number of Firm Shares set forth on Schedule A opposite the name of such Underwriter bears to the total number of Firm Shares.

(d) Public Offering of the Shares. The Representatives hereby advise the Company that the Underwriters intend to offer for sale to the public, as described in the Prospectus, their respective portions of the Shares as soon after this Agreement has been executed and the Registration Statement has been declared effective as the Representatives, in their sole judgment, have determined is advisable and practicable.

(e) Payment for the Shares. Payment for the Shares shall be made at the Closing Date (and, if applicable, at any Subsequent Closing Date) by wire transfer of immediately available funds to the order of the Company.

It is understood that the Representatives have been authorized, for their own account and the accounts of the several Underwriters, to accept delivery of and receipt for, and make payment of the purchase price for, the Firm Shares and any Optional Shares that the Underwriters have agreed to purchase. BAS and UBS, individually and not as the Representatives of the Underwriters, may (but shall not be obligated to) make payment for any Shares to be purchased by any Underwriter whose funds shall not have been received by the Representatives by the

Closing Date or any Subsequent Closing Date, as the case may be, for the account of such Underwriter, but any such payment shall not relieve such Underwriter from any of its obligations under this Agreement.

(f) Delivery of the Shares. Delivery of the Firm Shares and the Optional Shares shall be made through the facilities of The Depository Trust Company unless the Representatives shall otherwise instruct. Time shall be of the essence, and delivery at the time and place specified in this Agreement is a further condition to the obligations of the Underwriters.

(g) Delivery of Prospectus to the Underwriters. Not later than 10:00 a.m. on the second business day following the date the Shares are first released by the Underwriters for sale to the public, the Company shall deliver or cause to be delivered, copies of the Prospectus in such quantities and at such places as the Representatives shall reasonably request.

SECTION 3. Covenants.

The Company covenants and agrees with each Underwriter as follows:

(a) Representatives’ Review of Proposed Amendments and Supplements. During the period beginning on the Applicable Time and ending on the later of the Closing Date or such date, as in the reasonable opinion of counsel for the Company and the Underwriters, the Prospectus is no longer required by law to be delivered in connection with sales by an Underwriter or dealer, including in circumstances where such requirement may be satisfied pursuant to Rule 172 (the “Prospectus Delivery Period”), prior to amending or supplementing the Registration Statement, the Disclosure Package or the Prospectus, the Company shall furnish to the Representatives for review a copy of each such proposed amendment or supplement, and the Company shall not file or use any such proposed amendment or supplement to which the Representatives reasonably object.

(b) Securities Act Compliance. After the date of this Agreement until the end of the Prospectus Delivery Period, the Company shall promptly advise the Representatives in writing (i) when the Registration Statement, if not effective at the Execution Time, shall have become effective, (ii) of the receipt of any comments of, or requests for additional or supplemental information from, the Commission, (iii) of the time and date of any filing of any post-effective amendment to the Registration Statement or any amendment or supplement to any preliminary prospectus or the Prospectus, (iv) of the time and date that any post-effective amendment to the Registration Statement becomes effective and (v) of the issuance by the Commission of any stop order suspending the effectiveness of the Registration Statement or any post-effective amendment thereto or of any order or notice preventing or suspending the use of the Registration Statement, any preliminary prospectus or the Prospectus, or of any proceedings to remove, suspend or terminate from listing or quotation the Common Stock from any securities exchange upon which it is listed for trading or included or designated for quotation, or of the threatening or initiation of any proceedings for any of such purposes. The Company shall use its best efforts to prevent the issuance of any such stop order or prevention or suspension of such use. If the Commission shall enter any such stop order or order or notice of prevention or suspension at any time, the Company will use its best efforts to obtain the lifting of such order or notice at the earliest possible moment, or will file an amendment to the Registration Statement or a new

registration statement and use its best efforts to have such amendment or new registration statement declared effective as soon as practicable. Additionally, the Company agrees that it shall comply with the provisions of Rules 424(b) and 430A, as applicable, under the Securities Act, including with respect to the timely filing of documents thereunder, and will use its reasonable efforts to confirm that any filings made by the Company under such Rule 424(b) were received in a timely manner by the Commission.

(c) Exchange Act Compliance. During the Prospectus Delivery Period, the Company will file all documents required to be filed with the Commission pursuant to Section 13, 14 or 15 of the Exchange Act in the manner and within the time periods required by the Exchange Act.

(d) Amendments and Supplements to the Registration Statement, Disclosure Package, Prospectus and Other Securities Act Matters. If, during the Prospectus Delivery Period, any event or development shall occur or condition exist as a result of which the Disclosure Package or the Prospectus as then amended or supplemented would include any untrue statement of a material fact or omit to state any material fact necessary in order to make the statements therein in the light of the circumstances under which they were made or then prevailing, as the case may be, not misleading, or if it shall be necessary to amend or supplement the Disclosure Package or the Prospectus in order to make the statements therein, in the light of the circumstances under which they were made or then prevailing, as the case may be, not misleading, or if in the reasonable opinion of counsel for the Representatives it is otherwise necessary to amend or supplement the Registration Statement, the Disclosure Package or the Prospectus, including in connection with the delivery of the Prospectus, the Company agrees to (i) notify the Representatives of any such event or condition and (ii) promptly prepare (subject to Section 3(a) and 3(e) hereof), file with the Commission (and use its best efforts to have any amendment to the Registration Statement to be declared effective) and furnish at its own expense to the Underwriters, amendments or supplements to the Registration Statement, the Disclosure Package or the Prospectus necessary in order to make the statements in the Disclosure Package or the Prospectus as so amended or supplemented, in the light of the circumstances under which they were made or then prevailing, as the case may be, not misleading.

(e) Permitted Free Writing Prospectuses. The Company represents that it has not made, and agrees that, unless it obtains the prior consent of the Representatives, it will not make, any offer relating to the Shares that constitutes or would constitute an Issuer Free Writing Prospectus or that otherwise constitutes or would constitute a “free writing prospectus” (as defined in Rule 405 of the Securities Act) required to be filed by the Company with the Commission or retained by the Company under Rule 433 of the Securities Act; provided that the prior written consent of the Representatives hereto shall be deemed to have been given in respect of the Free Writing Prospectuses included in Schedule B hereto. Any such free writing prospectus consented to by the Representatives is hereinafter referred to as a “Permitted Free Writing Prospectus”. The Company agrees that (i) it has treated and will treat, as the case may be, each Permitted Free Writing Prospectus as an Issuer Free Writing Prospectus, and (ii) has complied and will comply, as the case may be, with the requirements of Rules 164 and 433 of the Securities Act applicable to any Permitted Free Writing Prospectus, including in respect of timely filing with the Commission, legending and record keeping.

(f) Copies of any Amendments and Supplements to the Prospectus. The Company agrees to furnish the Representatives, without charge, during the Prospectus Delivery Period, as many copies of the Prospectus and any amendments and supplements thereto and the Disclosure Package as the Representatives may reasonably request.

(g) Copies of the Registration Statement and the Prospectus. The Company will furnish to the Representatives and counsel for the Underwriters upon request signed copies of the Registration Statement (including exhibits thereto) and, during the Prospectus Delivery Period, as many copies of the preliminary prospectus included in the Disclosure Package and any other documents included in the Disclosure Package, the Prospectus and any amendments or supplements thereto as the Representatives may reasonably request.

(h) Blue Sky Compliance. The Company shall cooperate with the Representatives and counsel for the Underwriters to qualify or register the Shares for sale under (or obtain exemptions from the application of) the state securities or blue sky laws or Canadian provincial Securities laws or other foreign laws of those jurisdictions designated by the Representatives, shall comply with such laws and shall continue such qualifications, registrations and exemptions in effect so long as required for the distribution of the Shares. The Company shall not be required to qualify as a foreign corporation or to take any action that would subject it to general service of process in any such jurisdiction where it is not presently qualified or where it would be subject to taxation as a foreign corporation. The Company will advise the Representatives promptly of the suspension of the qualification or registration of (or any such exemption relating to) the Shares for offering, sale or trading in any jurisdiction or any initiation or threat of any proceeding for any such purpose, and in the event of the issuance of any order suspending such qualification, registration or exemption, the Company shall use its best efforts to obtain the withdrawal thereof at the earliest possible moment.

(i) Use of Proceeds. The Company intends to apply the net proceeds from the sale of the Shares sold by it in the manner described under the caption “Use of Proceeds” in each of the Disclosure Package and the Prospectus. Additionally, the Company shall report the use of proceeds from the issuance of the Shares as may be required under Rule 463 under the Securities Act.

(j) Transfer Agent. The Company shall engage and maintain, at its expense, a registrar and transfer agent for the Common Stock.

(k) Earnings Statement. As soon as practicable, the Company will make generally available to its security holders and to the Representatives an earnings statement (which need not be audited) covering the twelve-month period ending June 30, 2008 that satisfies the provisions of Section 11(a) of the Securities Act and Rule 158 under the Securities Act.

(l) Quotation. The Company will use its best efforts to include, subject to notice of issuance, the Shares on The Nasdaq Global Market.

(m) Agreement Not to Offer or Sell Additional Shares. During the period commencing on the date hereof and ending on the 180th day following the date hereof, the Company will not, without the prior written consent of the Representatives (which consent may be withheld at the

sole discretion of the Representatives), directly or indirectly, sell, offer, contract or grant any option to sell, pledge, transfer or establish an open “put equivalent position” or liquidate or decrease a “call equivalent position” within the meaning of Rule 16a-1(h) under the Exchange Act, or otherwise dispose of or transfer (or enter into any transaction which is designed to result in the disposition of), or announce the offering of, or file any registration statement under the Securities Act in respect of, any shares of Common Stock, options or warrants to acquire shares of the Common Stock or securities exchangeable or exercisable for or convertible into shares of Common Stock (other than as contemplated by this Agreement with respect to the Shares); provided, however, that the Company may: (i) file a registration statement on Form S-8, (ii) issue restricted shares of its Common Stock or options to purchase shares of its Common Stock, (iii) issue shares of its Common Stock or options to purchase shares of its Common Stock, or Common Stock upon exercise of options, pursuant to any stock option, stock bonus or other stock plan or arrangement described in the Prospectus, (iv) issue shares of Common Stock or securities exercisable for Common Stock (in an aggregate amount not to exceed, on an as-exercised basis, if applicable, 5% of our outstanding shares of common stock after giving effect to the issuance or sale of the common stock offered hereby) in connection with a strategic partnership, licensing, joint venture, collaboration, lending or similar arrangements, or in connection with the acquisition or license by the Company of any business, products or technologies, and (v) issue restricted shares of its Common Stock upon exercise of any warrants described in the Disclosure Package or the Prospectus, but with respect to each of clauses (i) through (v) above only if the holders of such shares, options, or shares issued upon exercise of such options or warrants, agree in writing not to sell, offer, dispose of or otherwise transfer any such shares or options during such 180-day period without the prior written consent of the Representatives (which consent may be withheld at the sole discretion of the Representatives). Notwithstanding the foregoing, if (x) during the last 17 days of the 180-day restricted period the Company issues an earnings release or material news or a material event relating to the Company occurs, or (y) prior to the expiration of the 180-day restricted period, the Company announces that it will release earnings results during the 16-day period beginning on the last day of the 180-day period, the restrictions imposed in this clause shall continue to apply until the expiration of the 18-day period beginning on the issuance of the earnings release or the occurrence of the material news or material event. The Company will provide the Representatives and any co-managers and each individual subject to the restricted period pursuant to the lockup letters described in Section 5(h) with prior notice of any such announcement that gives rise to an extension of the restricted period.

(n) Compliance with ▇▇▇▇▇▇▇▇-▇▇▇▇▇ Act. The Company will comply in all material respects with all applicable securities and other laws, rules and regulations, including, without limitation, the ▇▇▇▇▇▇▇▇-▇▇▇▇▇ Act, and use its best efforts to cause the Company’s directors and officers, in their capacities as such, to comply in all material respects with such laws, rules and regulations, including, without limitation, the provisions of the ▇▇▇▇▇▇▇▇-▇▇▇▇▇ Act.

(o) Future Reports to the Representatives. During the period of three years hereafter, to the extent such information is not available on the Commission’s website or the Company’s website, the Company will furnish to the BAS at ▇ ▇▇▇▇ ▇▇▇▇ ▇▇▇▇▇▇, ▇▇▇ ▇▇▇▇, ▇▇ ▇▇▇▇▇ Attention: Syndicate Department and UBS at ▇▇▇ ▇▇▇▇ ▇▇▇▇▇▇, ▇▇▇ ▇▇▇▇, ▇▇ ▇▇▇▇▇ Attention: Syndicate Department: (i) as soon as practicable after the end of each fiscal year, copies of the Annual Report of the Company containing the balance sheet of the Company as of the close of such fiscal year and statements of income, shareholders’ equity and cash flows for the year then ended and the opinion thereon of the Company’s independent public or certified public accountants; (ii) as soon

as practicable after the filing thereof, copies of each proxy statement, Annual Report on Form 10-K, Quarterly Report on Form 10-Q, Current Report on Form 8-K or other report filed by the Company with the Commission, the NASD or any securities exchange; and (iii) as soon as available, copies of any report or communication of the Company mailed generally to holders of its capital stock, provided that the filing of such reports and communications through the Commission’s ▇▇▇▇▇ system shall be deemed to satisfy this Section 3(o).

(p) No Manipulation of Price. The Company will not take, directly or indirectly, any action designed to cause or result in, or that has constituted or might reasonably be expected to constitute, under the Exchange Act or otherwise, the stabilization or manipulation of the price of any securities of the Company to facilitate the sale or resale of the Shares.

(q) Existing Lock-Up Agreements. The Company will use its best efforts to enforce all existing agreements between the Company and any of its security holders that prohibit the sale, transfer, assignment, pledge or hypothecation of any of the Company’s securities in connection with the Company’s initial public offering. In addition, the Company will direct the transfer agent to place stop transfer restrictions upon any such securities of the Company that are bound by such existing “lock-up” agreements for the duration of the periods contemplated in such agreements.

The Representatives, on behalf of the several Underwriters, may, in their sole discretion, waive in writing the performance by the Company of any one or more of the foregoing covenants or extend the time for their performance. Notwithstanding the foregoing, the Representatives, for the benefit of each of the other Underwriters, agree not to consent to any action proposed to be taken by the Company or any other holder of the Company’s securities that would otherwise be prohibited by, or to waive compliance by the Company or any such other security holder with the provisions of, Section 3(m) above or any lock-up agreement delivered pursuant to Section 5(h) below without giving each of the other Underwriters at least 17 days prior notice (or such shorter notice as each of the other Underwriters may deem acceptable to permit compliance with applicable provisions of NASD Conduct Rule 2711(f) restricting publication and distribution of research and public appearances by research analysts before and after the expiration, waiver or termination of a lock-up agreement).

Each Underwriter severally certifies to and covenants with the Company that it has not used and will not use, authorize use of, refer to, or participate in the planning for use of any “free writing prospectus”, as defined in Rule 405 under the Securities Act, other than (i) a free writing prospectus that contains no “issuer information” (as defined in Rule 433(h)(2) under the Securities Act) that was not included in the preliminary prospectus that is part of the Disclosure Package, (ii) any Free Writing Prospectus identified on Schedule B hereto, or (iii) any free writing prospectus prepared by such underwriter and approved by the Company in advance in writing, such approval not to be unreasonably withheld.

SECTION 4. Payment of Expenses. The Company agrees to pay all costs, fees and expenses incurred in connection with the performance of its obligations hereunder and in connection with the transactions contemplated hereby, including without limitation (i) all expenses incident to the issuance and delivery of the Shares (including all printing and engraving costs), (ii) all fees and expenses of the registrar and transfer agent of the Common Stock, (iii) all

necessary issue, transfer and other stamp taxes in connection with the issuance and sale of the Shares to the Underwriters, (iv) all fees and expenses of the Company’s counsel, independent public or certified public accountants and other advisors, (v) all costs and expenses incurred in connection with the preparation, printing, filing, shipping and distribution of the Registration Statement (including financial statements, exhibits, schedules, consents and certificates of experts), each Issuer Free Writing Prospectus, each preliminary prospectus and the Prospectus, and all amendments and supplements thereto, and this Agreement, (vi) all filing fees, reasonable attorneys’ fees and expenses incurred by the Company or the Underwriters in connection with qualifying or registering (or obtaining exemptions from the qualification or registration of) all or any part of the Shares for offer and sale under the state securities or blue sky laws or the provincial securities laws of Canada, and, if requested by the Representatives, preparing and printing a “Blue Sky Survey” or memorandum, and any supplements thereto, advising the Underwriters of such qualifications, registrations and exemptions, (vii) the filing fees incident to, and the reasonable fees and expenses of counsel for the Underwriters in connection with, the NASD’s review and approval of the Underwriters’ participation in the offering and distribution of the Shares, (viii) the fees and expenses associated with quotation of the Common Stock on The Nasdaq Global Market, (ix) all transportation and other expenses incurred in connection with presentations to prospective purchasers of the Shares, except that the Company and the Underwriters will each pay 50% of the cost of privately chartered airplanes used for such purposes and (x) all other fees, costs and expenses referred to in Item 13 of Part II of the Registration Statement. Except as provided in this Section 4, Section 6, Section 8 and Section 9 hereof, the Underwriters shall pay their own expenses, including the fees and disbursements of their counsel.

SECTION 5. Conditions of the Obligations of the Underwriters. The obligations of the several Underwriters to purchase and pay for the Shares as provided herein on the Closing Date and, with respect to the Optional Shares, any Subsequent Closing Date, shall be subject to the accuracy of the representations and warranties on the part of the Company set forth in Section 1 hereof as of the date hereof and as of the Closing Date as though then made and, with respect to the Optional Shares, as of any Subsequent Closing Date as though then made, to the accuracy of the statements of the Company made in any certificates pursuant to the provisions hereof, to the timely performance by the Company of its covenants and other obligations hereunder, and to each of the following additional conditions:

(a) Accountants’ Comfort Letter. On the date hereof, the Representatives shall have received from ▇▇▇▇▇ ▇▇▇▇▇▇▇▇, independent public accountants for the Company, a letter dated the date hereof addressed to the Underwriters, substantially in the form attached as Exhibit A, and from Deloitte & Touche LLP, former independent public accountant for the Company, a letter dated the date hereof addressed to the Underwriters, substantially in the form attached as Exhibit B.

(b) Compliance with Registration Requirements; No Stop Order; No Objection from NASD. For the period from and after effectiveness of this Agreement and prior to the Closing Date and, with respect to the Optional Shares, any Subsequent Closing Date:

(i) the Company shall have filed the Prospectus with the Commission (including the information required by Rule 430A under the Securities Act) in the manner and

within the time period required by Rule 424(b) under the Securities Act; or the Company shall have filed a post-effective amendment to the Registration Statement containing the information required by such Rule 430A, and such post-effective amendment shall have become effective;

(ii) all material required to be filed by the Company pursuant to Rule 433(d) under the Securities Act shall have been filed with the Commission within the applicable time periods prescribed for such filings under such Rule 433;

(iii) no stop order suspending the effectiveness of the Registration Statement, or any post-effective amendment to the Registration Statement, shall be in effect and no proceedings for such purpose shall have been instituted or threatened by the Commission; and

(iv) the NASD shall have raised no objection to the fairness and reasonableness of the underwriting terms and arrangements.

(c) No Material Adverse Change. For the period from and after the date of this Agreement and prior to the Closing Date and, with respect to the Optional Shares, any Subsequent Closing Date, in the judgment of the Representatives there shall not have occurred any Material Adverse Change.

(d) Opinion of Counsel for the Company. On each of the Closing Date and any Subsequent Closing Date, the Representatives shall have received the favorable opinion of Shearman & Sterling LLP, counsel for the Company, dated as of such Closing Date, substantially in the form attached as Exhibit C, the favorable opinion of in-house counsel for the Company, dated as of such Closing Date, substantially in the form attached as Exhibit D, the favorable opinion of Merchant & ▇▇▇▇▇ P.C., patent counsel for the Company, dated as of such Closing Date, substantially in the form attached as Exhibit E, and the favorable opinion of ▇▇▇▇▇ & ▇▇▇▇▇▇▇ LLP, regulatory counsel for the Company, dated as of such Closing Date, substantially in the form attached as Exhibit F.

(e) Opinion of Counsel for the Underwriters. On each of the Closing Date and any Subsequent Closing Date, the Representatives shall have received the favorable opinion of ▇▇▇▇▇ ▇▇▇▇ & ▇▇▇▇▇▇▇▇, counsel for the Underwriters, dated as of such Closing Date, in form and substance satisfactory to, and addressed to, the Representatives, with respect to the issuance and sale of the Shares, the Registration Statement, the Prospectus (together with any supplement thereto), the Disclosure Package and other related matters as the Representatives may reasonably require, and the Company shall have furnished to such counsel such documents as they reasonably request for the purpose of enabling them to pass upon such matters.

(f) Officers’ Certificate. On each of the Closing Date and any Subsequent Closing Date, the Representatives shall have received a written certificate executed by the Chairman of the Board, Chief Executive Officer or President of the Company and the Chief Financial Officer or Chief Accounting Officer of the Company, dated as of such Closing Date, to the effect that the signers of such certificate have examined the Registration Statement, the Prospectus and any amendment or supplement thereto, any Issuer Free Writing Prospectus and any amendment or

supplement thereto and this Agreement, to the effect set forth in subsections (b) and (c)(iii) of this Section 5, and further to the effect that:

(i) for the period from and after the date of this Agreement and prior to such Closing Date, there has not occurred any Material Adverse Change;

(ii) the representations, warranties and covenants of the Company set forth in Section 1 of this Agreement are true and correct on and as of the Closing Date with the same force and effect as though expressly made on and as of such Closing Date; and

(iii) the Company has complied with all the agreements hereunder and satisfied all the conditions on its part to be performed or satisfied hereunder at or prior to such Closing Date.

(g) Bring-down Comfort Letter. On each of the Closing Date and any Subsequent Closing Date, the Representatives shall have received from ▇▇▇▇▇ ▇▇▇▇▇▇▇▇, independent public accountants for the Company, a letter dated such date, in form and substance satisfactory to the Representatives, to the effect that they reaffirm the statements made in the letter furnished by them pursuant to subsection (a) of this Section 5, except that the specified date referred to therein for the carrying out of procedures shall be no more than three business days prior to the Closing Date or Subsequent Closing Date, as the case may be.

(h) Lock-Up Agreement from Certain Securityholders of the Company. On or prior to the date hereof, the Company shall have furnished to the Representatives an agreement in substantially the form of Exhibit G hereto (or in such other form separately agreed upon by the Representatives) from each person listed on Schedule D, and such agreement shall be in full force and effect on each of the Closing Date and any Subsequent Closing Date.

(i) Listing of Shares. The Shares shall have been authorized for quotation on The Nasdaq Global Market.

(j) Certificate of Chief Financial Officer. On the closing date, the Representatives shall have received a certificate, executed by the Chief Financial Officer of the Company and dated the date hereof, substantially in the form attached as Exhibit H.

(k) Additional Documents. On or before each of the Closing Date and any Subsequent Closing Date, the Representatives and counsel for the Underwriters shall have received such information, certificates and other documents as they may reasonably require for the purposes of enabling them to pass upon the issuance and sale of the Shares as contemplated herein, or in order to evidence the accuracy of any of the representations and warranties, or the satisfaction of any of the conditions or agreements, herein contained.

If any condition specified in this Section 5 is not satisfied when and as required to be satisfied, this Agreement may be terminated by the Representatives by written notice to the Company at any time on or prior to the Closing Date and, with respect to the Optional Shares, at any time prior to the applicable Subsequent Closing Date, which termination shall be without liability on the part of any party to any other party, except that Section 4, Section 6, Section 8 and Section 9 shall at all times be effective and shall survive such termination.

SECTION 6. Reimbursement of Underwriters’ Expenses. If this Agreement is terminated by the Representatives pursuant to Section 5, Section 7 or Section 11, or if the sale to the Underwriters of the Shares on the Closing Date is not consummated because of any refusal,

inability or failure on the part of the Company to perform any agreement herein or to comply with any provision hereof, the Company agrees to reimburse the Representatives and the other Underwriters (or such Underwriters as have terminated this Agreement with respect to themselves), severally, upon demand for all out-of-pocket expenses that shall have been reasonably incurred by the Representatives and the Underwriters in connection with the proposed purchase and the offering and sale of the Shares, including but not limited to reasonable fees and disbursements of counsel, printing expenses, travel expenses, postage, facsimile and telephone charges.

SECTION 7. Effectiveness of this Agreement. This Agreement shall not become effective until the later of (i) the execution of this Agreement by the parties hereto and (ii) notification by the Commission to the Company and the Representatives of the effectiveness of the Registration Statement under the Securities Act.

Prior to such effectiveness, this Agreement may be terminated by any party by notice to each of the other parties hereto, and any such termination shall be without liability on the part of (a) the Company to any Underwriter, except that the Company shall be obligated to reimburse the expenses of the Representatives and the Underwriters pursuant to Sections 4 and 6 hereof or (b) of any Underwriter to the Company.

SECTION 8. Indemnification.

(a) Indemnification of the Underwriters. The Company agrees to indemnify and hold harmless each Underwriter, its directors, officers, employees and agents, and each person, if any, who controls any Underwriter within the meaning of the Securities Act and the Exchange Act against any loss, claim, damage, liability or expense, as incurred, to which such Underwriter or such controlling person may become subject, insofar as such loss, claim, damage, liability or expense (or actions in respect thereof as contemplated below) arises out of or is based (i) upon any untrue statement or alleged untrue statement of a material fact contained in the Registration Statement, or any amendment thereto, including any information deemed to be a part thereof pursuant to Rule 430A, Rule 430B or Rule 430C under the Securities Act, or the omission or alleged omission therefrom of a material fact required to be stated therein or necessary to make the statements therein not misleading; or (ii) upon any untrue statement or alleged untrue statement of a material fact contained in any Issuer Free Writing Prospectus, any preliminary prospectus or the Prospectus (or any amendment or supplement thereto) or the omission or alleged omission therefrom of a material fact necessary in order to make the statements therein, in the light of the circumstances under which they were made, not misleading, and to reimburse each Underwriter, its officers, directors, employees, agents and each such controlling person for any and all expenses (including the fees and disbursements of one counsel chosen by the Representatives) as such expenses are reasonably incurred by such Underwriter, or its officers, directors, employees and agents or such controlling person in connection with investigating, defending, settling, compromising or paying any such loss, claim, damage, liability, expense or action; provided, however, that the foregoing indemnity agreement shall not apply to any loss, claim, damage, liability or expense to the extent, but only to the extent, arising out of or based upon any untrue statement or alleged untrue statement or omission or alleged omission made in reliance upon and in conformity with written information furnished to the Company by the Representatives expressly for use in the Registration Statement, any Issuer Free Writing

Prospectus, any preliminary prospectus or the Prospectus (or any amendment or supplement thereto). The indemnity agreement set forth in this Section 8(a) shall be in addition to any liabilities that the Company may otherwise have.

(b) Indemnification of the Company, its Directors and Officers. Each Underwriter agrees, severally and not jointly, to indemnify and hold harmless the Company, each of its directors, each of its officers who signed the Registration Statement and each person, if any, who controls the Company within the meaning of the Securities Act or the Exchange Act, against any loss, claim, damage, liability or expense, as incurred, to which the Company, or any such director, officer or controlling person may become subject, insofar as such loss, claim, damage, liability or expense (or actions in respect thereof as contemplated below) arises out of or is based upon any untrue or alleged untrue statement of a material fact contained in the Registration Statement, any Issuer Free Writing Prospectus, any preliminary prospectus or the Prospectus (or any amendment or supplement thereto), or arises out of or is based upon the omission or alleged omission to state therein a material fact required to be stated therein or necessary to make the statements therein not misleading, in each case to the extent, and only to the extent, that such untrue statement or alleged untrue statement or omission or alleged omission was made in the Registration Statement, any Issuer Free Writing Prospectus, any preliminary prospectus or the Prospectus (or any amendment or supplement thereto), in reliance upon and in conformity with written information furnished to the Company by the Representatives expressly for use therein; and to reimburse the Company, or any such director, officer or controlling person for any legal and other expense reasonably incurred by the Company, or any such director, officer or controlling person in connection with investigating, defending, settling, compromising or paying any such loss, claim, damage, liability, expense or action. The Company hereby acknowledges that the only information that the Underwriters have furnished to the Company expressly for use in the Registration Statement, any Issuer Free Writing Prospectus, any preliminary prospectus or the Prospectus (or any amendment or supplement thereto) are the statements set forth in (A) the table in the first paragraph, (B) the first four sentences of the third paragraph (C) the subsection “Stabilization”, (D) the subsection “Discretionary Accounts”, and (E) the subsection “Online Offering”, all under the caption “Underwriting” in the Prospectus. The indemnity agreement set forth in this Section 8(b) shall be in addition to any liabilities that each Underwriter may otherwise have.

(c) Notifications and Other Indemnification Procedures. Promptly after receipt by an indemnified party under this Section 8 of notice of the commencement of any action, such indemnified party will, if a claim in respect thereof is to be made against an indemnifying party under this Section 8, notify the indemnifying party in writing of the commencement thereof; but the failure to so notify the indemnifying party (i) will not relieve it from liability under paragraph (a) or (b) above unless and to the extent it did not otherwise learn of such action and such failure results in the forfeiture by the indemnifying party of substantial rights and defenses and (ii) will not, in any event, relieve the indemnifying party from any liability other than the indemnification obligation provided in paragraph (a) or (b) above. In case any such action is brought against any indemnified party and such indemnified party seeks or intends to seek indemnity from an indemnifying party, the indemnifying party will be entitled to participate in, and, to the extent that it shall elect, jointly with all other indemnifying parties similarly notified, by written notice delivered to the indemnified party promptly after receiving the aforesaid notice from such indemnified party, to assume the defense thereof with counsel reasonably satisfactory to such

indemnified party; provided, however, if the defendants in any such action include both the indemnified party and the indemnifying party and the indemnified party shall have reasonably concluded that a conflict may arise between the positions of the indemnifying party and the indemnified party in conducting the defense of any such action or that there may be legal defenses available to it and/or other indemnified parties that are different from or additional to those available to the indemnifying party, the indemnified party or parties shall have the right to select separate counsel to assume such legal defenses and to otherwise participate in the defense of such action on behalf of such indemnified party or parties. Upon receipt of notice from the indemnifying party to such indemnified party of such indemnifying party’s election so to assume the defense of such action and approval by the indemnified party of counsel, the indemnifying party will not be liable to such indemnified party under this Section 8 for any legal or other expenses subsequently incurred by such indemnified party in connection with the defense thereof unless (i) the indemnified party shall have employed separate counsel in accordance with the proviso to the preceding sentence (it being understood, however, that the indemnifying party shall not be liable for the expenses of more than one separate counsel (other than one local counsel), reasonably approved by the indemnifying party (or by the Representatives in the case of Section 8(b)), representing the indemnified parties who are parties to such action) or (ii) the indemnifying party shall not have employed counsel satisfactory to the indemnified party to represent the indemnified party within a reasonable time after notice of commencement of the action, in each of which cases the fees and expenses of counsel shall be at the expense of the indemnifying party.

(d) Settlements. The indemnifying party under this Section 8 shall not be liable for any settlement of any proceeding effected without its written consent, but if settled with such consent or if there be a final judgment for the plaintiff, the indemnifying party agrees to indemnify the indemnified party against any loss, claim, damage, liability or expense by reason of such settlement or judgment. Notwithstanding the foregoing sentence, if at any time an indemnified party shall have requested an indemnifying party to reimburse the indemnified party for fees and expenses of counsel as contemplated by Section 8(c) hereof, the indemnifying party agrees that it shall be liable for any settlement of any proceeding effected without its written consent if (i) such settlement is entered into more than 45 days after receipt by such indemnifying party of the aforesaid request and (ii) such indemnifying party shall not have reimbursed the indemnified party in accordance with such request prior to the date of such settlement. No indemnifying party shall, without the prior written consent of the indemnified party, which consent shall not be unreasonably withheld or delayed, effect any settlement, compromise or consent to the entry of judgment in any pending or threatened action, suit or proceeding in respect of which any indemnified party is or could have been a party and indemnity was or could have been sought hereunder by such indemnified party, unless such settlement, compromise or consent (i) includes an unconditional release of such indemnified party from all liability on claims that are the subject matter of such action, suit or proceeding and (ii) does not include a statement as to or an admission of fault, culpability or a failure to act, by or on behalf of any indemnified party.

SECTION 9. Contribution. If the indemnification provided for in Section 8 is for any reason unavailable to or otherwise insufficient to hold harmless an indemnified party in respect of any losses, claims, damages, liabilities or expenses referred to therein, then each indemnifying party shall contribute to the aggregate amount paid or payable by such indemnified party, as incurred, as a result of any losses, claims, damages, liabilities or expenses referred to therein (i)

in such proportion as is appropriate to reflect the relative benefits received by the Company, on the one hand, and the Underwriters, on the other hand, from the offering of the Shares pursuant to this Agreement or (ii) if the allocation provided by clause (i) above is not permitted by applicable law, in such proportion as is appropriate to reflect not only the relative benefits referred to in clause (i) above but also the relative fault of the Company, on the one hand, and the Underwriters, on the other hand, in connection with the statements or omissions or inaccuracies in the representations and warranties herein which resulted in such losses, claims, damages, liabilities or expenses, as well as any other relevant equitable considerations. The relative benefits received by the Company, on the one hand, and the Underwriters, on the other hand, in connection with the offering of the Shares pursuant to this Agreement shall be deemed to be in the same respective proportions as the total net proceeds from the offering of the Shares pursuant to this Agreement (before deducting expenses) received by the Company, and the total underwriting discount received by the Underwriters, in each case as set forth on the front cover page of the Prospectus bear to the aggregate initial public offering price of the Shares as set forth on such cover. The relative fault of the Company, on the one hand, and the Underwriters, on the other hand, shall be determined by reference to, among other things, whether any such untrue or alleged untrue statement of a material fact or omission or alleged omission to state a material fact or any such inaccurate or alleged inaccurate representation or warranty relates to information supplied by the Company, on the one hand, or the Underwriters, on the other hand, and the parties’ relative intent, knowledge, access to information and opportunity to correct or prevent such statement or omission.

The amount paid or payable by a party as a result of the losses, claims, damages, liabilities and expenses referred to above shall be deemed to include, subject to the limitations set forth in Section 8(c), any legal or other fees or expenses reasonably incurred by such party in connection with investigating or defending any action or claim. The provisions set forth in Section 8(c) with respect to notice of commencement of any action shall apply if a claim for contribution is to be made under this Section 9; provided, however, that no additional notice shall be required with respect to any action for which notice has been given under Section 8(c) for purposes of indemnification.

The Company and the Underwriters agree that it would not be just and equitable if contribution pursuant to this Section 9 were determined by pro rata allocation (even if the Underwriters were treated as one entity for such purpose) or by any other method of allocation which does not take account of the equitable considerations referred to in this Section 9.

Notwithstanding the provisions of this Section 9, no Underwriter shall be required to contribute any amount in excess of the underwriting commissions received by such Underwriter in connection with the Shares underwritten by it and distributed to the public. No person guilty of fraudulent misrepresentation (within the meaning of Section 11(f) of the Securities Act) shall be entitled to contribution from any person who was not guilty of such fraudulent misrepresentation. The Underwriters’ obligations to contribute pursuant to this Section 9 are several, and not joint, in proportion to their respective underwriting commitments as set forth opposite their names in Schedule A. For purposes of this Section 9, each director, officer, employee and agent of an Underwriter and each person, if any, who controls an Underwriter within the meaning of the Securities Act and the Exchange Act shall have the same rights to contribution as such Underwriter, and each director of the Company, each officer of the

Company who signed the Registration Statement and each person, if any, who controls the Company within the meaning of the Securities Act and the Exchange Act shall have the same rights to contribution as the Company.

SECTION 10. Default of One or More of the Several Underwriters. If, on the Closing Date or a Subsequent Closing Date, as the case may be, any one or more of the several Underwriters shall fail or refuse to purchase Shares that it or they have agreed to purchase hereunder on such date, and the aggregate number of Shares which such defaulting Underwriter or Underwriters agreed but failed or refused to purchase does not exceed 10% of the aggregate number of the Shares to be purchased on such date, the other Underwriters shall be obligated, severally, in the proportions that the number of Firm Shares set forth opposite their respective names on Schedule A bears to the aggregate number of Firm Shares set forth opposite the names of all such non-defaulting Underwriters, or in such other proportions as may be specified by the Representatives with the consent of the non-defaulting Underwriters, to purchase the Shares which such defaulting Underwriter or Underwriters agreed but failed or refused to purchase on such date. If, on the Closing Date or a Subsequent Closing Date, as the case may be, any one or more of the Underwriters shall fail or refuse to purchase Shares and the aggregate number of Shares with respect to which such default occurs exceeds 10% of the aggregate number of Shares to be purchased on such date, and arrangements satisfactory to the Representatives and the Company for the purchase of such Shares are not made within 48 hours after such default, this Agreement shall terminate without liability of any party to any other party except that the provisions of Section 4, Section 8 and Section 9 shall at all times be effective and shall survive such termination. In any such case either the Representatives or the Company shall have the right to postpone the Closing Date or a Subsequent Closing Date, as the case may be, but in no event for longer than seven days in order that the required changes, if any, to the Registration Statement and the Prospectus or any other documents or arrangements may be effected.

As used in this Agreement, the term “Underwriter” shall be deemed to include any person substituted for a defaulting Underwriter under this Section 10. Any action taken under this Section 10 shall not relieve any defaulting Underwriter from liability in respect of any default of such Underwriter under this Agreement.

SECTION 11. Termination of this Agreement. Prior to the Closing Date, this Agreement may be terminated by the Representatives by notice given to the Company if at any time (i) trading or quotation in any of the Company’s securities shall have been suspended or limited by the Commission or by The Nasdaq Global Market, or trading in securities generally on the New York Stock Exchange or The Nasdaq Global Market shall have been suspended or limited, or minimum or maximum prices shall have been generally established on any of such stock exchanges by the Commission or the NASD; (ii) a general banking moratorium shall have been declared by federal or New York authorities or a material disruption in commercial banking or securities settlement or clearance services in the United States has occurred; or (iii) there shall have occurred any outbreak or escalation of national or international hostilities or any crisis or calamity, or any change in the United States or international financial markets, or any substantial change or development involving a prospective substantial change in United States’ or international political, financial or economic conditions, as in the judgment of the Representatives is material and adverse and makes it impracticable or inadvisable to market the Shares in the manner and on the terms described in the Prospectus or to enforce contracts for the

sale of securities. Any termination pursuant to this Section 11 shall be without liability on the part of (a) the Company to any Underwriter, except that the Company shall be obligated to reimburse the expenses of the Representatives and the Underwriters pursuant to Sections 4 and 6 hereof or (b) any Underwriter to the Company.

SECTION 12. No Advisory or Fiduciary Responsibility. The Company acknowledges and agrees that: (i) the purchase and sale of the Securities pursuant to this Agreement, including the determination of the public offering price of the Securities and any related discounts and commissions, is an arm’s-length commercial transaction between the Company, on the one hand, and the several Underwriters, on the other hand, and the Company is capable of evaluating and understanding and understands and accepts the terms, risks and conditions of the transactions contemplated by this Agreement; (ii) in connection with each transaction contemplated hereby and the process leading to such transaction each Underwriter is and has been acting solely as a principal and is not the financial advisor, agent or fiduciary of the Company or its affiliates, shareholders, creditors or employees or any other party; (iii) no Underwriter has assumed or will assume an advisory, agency or fiduciary responsibility in favor of the Company with respect to any of the transactions contemplated hereby or the process leading thereto (irrespective of whether such Underwriter has advised or is currently advising the Company on other matters) and no Underwriter has any obligation to the Company with respect to the offering contemplated hereby except the obligations expressly set forth in this Agreement; (iv) the several Underwriters and their respective affiliates may be engaged in a broad range of transactions that involve interests that differ from those of the Company and that the several Underwriters have no obligation to disclose any of such interests by virtue of any advisory, agency or fiduciary relationship; and (v) the Underwriters have not provided any legal, accounting, regulatory or tax advice with respect to the offering contemplated hereby and the Company has consulted its own legal, accounting, regulatory and tax advisors to the extent it deemed appropriate.

This Agreement supersedes all prior agreements and understandings (whether written or oral) between the Company and the several Underwriters, or any of them, with respect to the subject matter hereof. The Company hereby waives and releases, to the fullest extent permitted by law, any claims that the Company may have against the several Underwriters with respect to any breach or alleged breach of agency or fiduciary duty.

SECTION 13. Representations and Indemnities to Survive Delivery. The respective indemnities, agreements, representations, warranties and other statements of the Company, of its officers and of the several Underwriters set forth in or made pursuant to this Agreement (i) will remain operative and in full force and effect, regardless of any (A) investigation, or statement as to the results thereof, made by or on behalf of any Underwriter, the officers or employees of any Underwriter, or the Company, the officers or employees of the Company, or any person controlling the Company, as the case may be or (B) acceptance of the Shares and payment for them hereunder and (ii) will survive delivery of and payment for the Shares sold hereunder and any termination of this Agreement.

SECTION 14. Notices. All communications hereunder shall be in writing and shall be mailed, hand delivered or telecopied and confirmed to the parties hereto as follows:

If to the Representatives:

Banc of America Securities LLC

▇ ▇▇▇▇ ▇▇^▇▇ ▇▇▇▇▇▇

▇▇▇ ▇▇▇▇, ▇▇▇ ▇▇▇▇ ▇▇▇▇▇

Facsimile: (▇▇▇) ▇▇▇-▇▇▇▇

Attention: Syndicate Department

UBS Securities LLC

▇▇▇ ▇▇▇▇ ▇▇▇▇▇▇

▇▇▇ ▇▇▇▇, ▇▇ ▇▇▇▇▇

Facsimile: (▇▇▇) ▇▇▇-▇▇▇▇

Attention: Syndicate Department

with a copy to:

▇▇▇▇▇ ▇▇▇▇ & ▇▇▇▇▇▇▇▇

▇▇▇ ▇▇▇▇▇▇▇▇▇ ▇▇▇▇▇▇

▇▇▇ ▇▇▇▇, ▇▇▇ ▇▇▇▇ ▇▇▇▇▇

Facsimile: 212-450-3800

Attention: ▇▇▇▇▇▇▇ ▇. ▇▇▇▇▇▇▇

If to the Company:

Pharmasset, Inc.

▇▇▇-▇ ▇▇▇▇▇▇▇ ▇▇▇▇ ▇▇▇▇

▇▇▇▇▇▇▇▇▇, ▇▇▇ ▇▇▇▇▇▇ ▇▇▇▇▇

Facsimile: (▇▇▇) ▇▇▇-▇▇▇▇

Attention: ▇▇▇▇▇ ▇▇▇▇▇▇▇

with a copy to:

Shearman & Sterling LLP

▇▇▇ ▇▇▇▇▇▇▇▇▇ ▇▇▇▇▇▇

▇▇▇ ▇▇▇▇, ▇▇▇ ▇▇▇▇ ▇▇▇▇▇

Facsimile: 212-848-7179

Attention: ▇▇▇▇▇▇▇▇ ▇▇▇▇▇▇▇

Any party hereto may change the address for receipt of communications by giving written notice to the others.

SECTION 15. Successors. This Agreement will inure to the benefit of and be binding upon the parties hereto, including any substitute Underwriters pursuant to Section 10 hereof, and to the benefit of (i) the Company, its directors, any person who controls the Company within the meaning of the Securities Act and the Exchange Act and any officer of the Company who signs the Registration Statement, (ii) the Underwriters, the officers, directors, employees and agents of the Underwriters, and each person, if any, who controls any Underwriter within the meaning of the Securities Act and the Exchange Act and (iv) the respective successors and assigns of any of the above, all as and to the extent provided in this Agreement, and no other person shall acquire

or have any right under or by virtue of this Agreement. The term “successors and assigns” shall not include a purchaser of any of the Shares from any of the several Underwriters merely because of such purchase.

SECTION 16. Partial Unenforceability. The invalidity or unenforceability of any Section, paragraph or provision of this Agreement shall not affect the validity or enforceability of any other Section, paragraph or provision hereof. If any Section, paragraph or provision of this Agreement is for any reason determined to be invalid or unenforceable, there shall be deemed to be made such minor changes (and only such minor changes) as are necessary to make it valid and enforceable.

SECTION 17. Governing Law Provisions. THIS AGREEMENT SHALL BE GOVERNED BY, AND CONSTRUED IN ACCORDANCE WITH THE LAWS OF THE STATE OF NEW YORK APPLICABLE TO AGREEMENTS MADE AND TO BE PERFORMED IN SUCH STATE.

SECTION 18. Submission to Jurisdiction. Any legal suit, action or proceeding arising out of or based upon this Agreement or the transactions contemplated hereby (“Related Proceedings”) may be instituted in the federal courts of the United States of America located in the City and County of New York, Borough of Manhattan, or the courts of the State of New York in each case located in the City and County of New York, Borough of Manhattan (collectively, the “Specified Courts”), and each party irrevocably submits to the exclusive jurisdiction (except for proceedings instituted in regard to the enforcement of a judgment of any such court (a “Related Judgment”), as to which such jurisdiction is non-exclusive) of such courts in any such suit, action or proceeding. Service of any process, summons, notice or document by mail to such party’s address set forth above shall be effective service of process for any suit, action or other proceeding brought in any such court. The parties irrevocably and unconditionally waive any objection to the laying of venue of any suit, action or other proceeding in the Specified Courts and irrevocably and unconditionally waive and agree not to plead or claim in any such court that any such suit, action or other proceeding brought in any such court has been brought in an inconvenient forum. Each Underwriter and the Company (on its behalf and, to the extent permitted by applicable law, on behalf of its stockholders and affiliates) waive all right to trial by jury in any action, proceeding or counterclaim (whether based upon contract, tort or otherwise) in any way arising out of or relating to this Agreement.

SECTION 19. General Provisions. This Agreement constitutes the entire agreement of the parties to this Agreement and supersedes all prior written or oral and all contemporaneous oral agreements, understandings and negotiations with respect to the subject matter hereof. This Agreement may be executed in two or more counterparts, each one of which shall be an original, with the same effect as if the signatures thereto and hereto were upon the same instrument. This Agreement may not be amended or modified unless in writing by all of the parties hereto, and no condition herein (express or implied) may be waived unless waived in writing by each party whom the condition is meant to benefit. The Section headings herein are for the convenience of the parties only and shall not affect the construction or interpretation of this Agreement.

Each of the parties hereto acknowledges that it is a sophisticated business person who was adequately represented by counsel during negotiations regarding the provisions hereof,

including, without limitation, the indemnification provisions of Section 8 and the contribution provisions of Section 9, and is fully informed regarding said provisions. Each of the parties hereto further acknowledges that the provisions of Sections 8 and 9 hereto fairly allocate the risks in light of the ability of the parties to investigate the Company, its affairs and its business in order to assure that adequate disclosure has been made in the Registration Statement, any preliminary prospectus and the Prospectus (and any amendments and supplements thereto), as required by the Securities Act and the Exchange Act.

If the foregoing is in accordance with your understanding of our agreement, kindly sign and return to the Company the enclosed copies hereof, whereupon this instrument, along with all counterparts hereof, shall become a binding agreement in accordance with its terms.


Very truly yours,

PHARMASSET, INC.

By:
		Name:
		Title:

The foregoing Underwriting Agreement is hereby confirmed and accepted by the Representatives as of the date first above written.


BANC OF AMERICA SECURITIES LLC UBS SECURITIES LLC

		Acting as Representatives of the several Underwriters named in the attached Schedule A.

By:		BANC OF AMERICA SECURITIES LLC

By:
		Name:
		Title:

By:		UBS SECURITIES LLC

By:
		Name:
		Title:

By:
		Name:
		Title:

SCHEDULE A


Underwriters	Number of Firm Shares to be Purchased
Banc of America Securities LLC	[___	]
UBS Securities LLC	[___	]
JMP Securities LLC	[___	]
Total	[___	]

SCHEDULE B

Schedule of Free Writing Prospectuses included in the Disclosure Package

SCHEDULE C

Number and Price of Shares

Price per Share to the public: $[ ]

Number of Firm Shares: [ ] shares

Number of Additional Shares (if known): [ ] shares.

SCHEDULE D

LIST OF PARTIES TO EXECUTE LOCK-UP AGREEMENTS


Name		Position
1. ▇. ▇▇▇▇▇▇▇▇ Price		President, Chief Executive Officer and Director

2. ▇▇▇▇ ▇▇▇▇▇▇▇▇▇▇		Executive Vice President and Chief Financial Officer

3. ▇▇▇▇▇▇▇ ▇. ▇▇▇▇		Executive Vice President, Pharmaceutical Research

4. ▇▇▇▇ De La ▇▇▇▇		Senior Vice President, Business Development & Scientific Affairs

5. ▇▇▇▇▇▇ ▇▇▇▇▇▇		Vice President, Manufacturing

6. ▇▇▇▇ ▇▇ ▇▇▇▇▇		Vice President, Regulatory Affairs

7. ▇▇▇▇▇▇▇ ▇. ▇▇▇▇▇▇		Vice President, Biological Sciences

8. ▇▇▇▇ ▇▇▇▇		Vice President, Project & Alliance Management

9. ▇▇▇▇ ▇. ▇▇▇▇▇▇▇		Vice President, Accounting & Administration

10. ▇▇▇▇ ▇. ▇▇▇▇▇▇		Vice President, Investor Relations & Corporate Communications

11. ▇▇▇▇▇▇▇ ▇. Sofia		Vice President, Chemistry

12. G. ▇▇▇▇▇▇ ▇▇▇▇▇▇▇		Chairman of the Board and Director

13. ▇▇▇▇▇▇▇ ▇. ▇▇▇▇▇▇		Director

14. Ansbert ▇. ▇▇▇▇▇▇▇		Director

15. ▇▇▇▇▇▇▇▇▇ ▇▇▇▇		Director


Name		Position
16. ▇▇▇▇▇▇ ▇. ▇▇▇▇		Director

17. ▇▇▇▇▇▇▇ ▇. ▇▇▇▇▇▇		Director

18. ▇▇▇▇▇▇ ▇. ▇▇▇▇▇▇▇▇▇▇		Director

19. BB BioVentures L.P.		Shareholder (Common, B, D, D-1)

20. MPM Asset Management Investors 1999 LLC		Shareholder (Common, B, D, D-1)

21. MPM BioVentures Parallel Fund, L.P.		Shareholder (Common, B, D, D-1)

22. MPM BioVentures III, L.P.		Shareholder (Common, D, D-1)

23. MPM BioVentures III-QP, L.P.		Shareholder (Common, D, D-1)

24. MPM BioVentures III GMBH & Co. Beteiligungs KG		Shareholder (Common, D, D-1)

25. MPM BioVentures III Parallel Fund, L.P.		Shareholder (Common, D, D-1)

26. MPM Asset Management Investors 2004 BVIII LLC		Shareholder (Common, D, D-1)

27. ▇▇▇▇▇▇▇ ▇. ▇▇▇▇▇▇▇▇		Shareholder (Common, A)

28. TVM ▇▇ ▇▇▇▇ & ▇▇. ▇▇		▇▇▇▇▇▇▇▇▇▇▇ (▇▇▇▇▇▇, ▇, ▇-▇)

▇▇. TMV Life Science Ventures GMBH & Co. KG		Shareholder (Common, D, D-1)

30. ▇▇▇▇▇▇▇ Life Sciences Capital Fund, L.P.		Shareholder (Common, D, D-1)

31. ▇▇▇▇▇▇▇ Indiana Life Sciences Capital Fund, L.P.		Shareholder (Common, D, D-1)

32. MDS Life Sciences Technology Fund II (Quebec Limited Partnership)		Shareholder (Common, D, D-1)


Name		Position
33. MLII Co-Investment Fund NC Limited Partnership		Shareholder (Common, D, D-1)

34. MDS Life Sciences Technology Fund II Limited Partnership		Shareholder (Common, D, D-1)

35. ▇▇▇▇▇▇▇▇-▇▇ ▇▇▇▇▇ Inc.		Shareholder (R)

36. ▇▇▇▇▇ ▇. ▇▇▇		Shareholder (Common, A)

37. CDIB BioScience Ventures I, Inc.		Shareholder (Common, D, D-1)

38. Emory University		Shareholder (Common)

39. Idenix Pharmaceuticals, Inc.		Shareholder (A)

40. ▇▇▇▇-▇▇▇▇▇▇ Sommadossi		Shareholder (Common, A)

41. ▇▇▇▇▇ ▇. Rabi		Shareholder (A)

42. ▇▇▇▇▇▇ ▇▇▇▇▇▇		Shareholder (Common, A)

43. ▇▇▇▇▇▇▇ ▇. ▇▇▇▇▇▇▇▇▇		Shareholder (Common, A)

44. ▇▇▇▇▇▇▇▇▇ ▇. ▇▇▇▇▇▇▇▇▇▇		Shareholder (Common)

45. Junxing Shi		Shareholder (Common, A)

46. ▇▇▇▇▇▇▇ ▇▇▇▇▇		Director

47. M. ▇▇▇▇▇▇▇▇ ▇▇▇▇▇▇		Vice President, Clinical Development and Chief Medical Officer

48. ▇▇▇▇▇▇▇ ▇▇▇▇▇▇▇		Vice President, Clinical Pharmacology

49. ▇▇▇▇▇▇▇ ▇▇▇▇▇▇▇		Shareholder (Common)

50. ▇▇▇▇▇▇▇ ▇▇▇▇▇▇▇▇		Shareholder (Common)

51. ▇▇▇▇▇▇ ▇▇▇		Shareholder (Common, A)


Name		Position
52. ▇▇▇▇▇ ▇▇▇▇ ▇▇▇▇▇▇▇▇		Shareholder (Common)

53. ▇▇▇▇▇▇▇ ▇ ▇▇▇▇▇▇▇▇ (▇▇▇▇▇▇▇▇)		Shareholder (Common)

54. ▇▇▇▇▇▇ ▇▇▇▇▇▇▇▇		Shareholder (Common)

55. ▇▇▇ ▇▇▇▇▇▇▇▇▇▇		Shareholder (Common)

56. ▇▇▇▇▇▇ ▇▇▇▇▇		Current Staff

57. ▇▇▇ ▇▇▇▇▇		Current Staff

58. ▇. ▇▇▇▇▇▇▇ ▇▇▇▇ ▇▇▇▇▇		Shareholder (Common)

59. ▇▇▇▇▇ ▇▇▇▇▇▇▇		Associate Director, Legal Affairs

60. ▇▇▇▇ ▇▇▇▇▇▇▇▇		Shareholder (Common)

61. F. ▇▇▇▇▇▇▇ ▇▇▇▇▇▇▇▇		Shareholder (Common)

62. ▇▇▇▇▇ ▇▇▇▇		Current Staff

63. ▇▇▇ ▇. ▇▇▇▇▇▇▇		Shareholder (Common)

64. ▇▇▇▇▇-▇▇▇▇ ▇▇▇▇		Current Staff

65. Mahmud H. el Kauni		Shareholder (Common, A)

66. ▇▇▇▇▇ ▇▇▇ ▇▇▇▇▇▇		Shareholder (Common, A)

67. ▇▇▇▇▇▇ ▇▇▇▇▇▇▇▇		Shareholder (Common)

68. ▇▇▇▇▇ ▇▇▇▇▇▇▇▇▇▇▇ ▇▇▇▇▇▇		Current Staff

69. ▇▇▇▇-▇▇▇▇▇ ▇▇▇▇▇▇		Shareholder (Common)

70. ▇▇▇▇▇ ▇▇▇▇▇▇		Current Staff

71. ▇▇▇▇ ▇▇▇▇		Shareholder (Common, A)

72. ▇▇▇▇▇ ▇▇▇▇ ▇▇▇▇▇▇		Current Staff


Name		Position
73. ▇▇▇▇ ▇. ▇▇▇▇▇▇▇		Current Staff

74. ▇▇▇▇ ▇▇▇▇▇▇▇		Shareholder (Common)

75. ▇▇▇▇▇▇▇▇ ▇▇▇▇▇▇▇▇▇▇		Shareholder (Common)

76. ▇▇▇▇▇▇▇ ▇▇▇▇▇▇		Shareholder (Common)

77. ▇▇▇▇▇▇▇▇ ▇▇▇▇▇▇▇		Current Staff

78. Lieven Stuyver		Shareholder (Common)

79. University of Georgia Research Foundation, Inc.		Shareholder (Common)

80. ▇▇▇▇▇▇▇ ▇▇▇▇▇▇▇▇▇		Shareholder (Common)

81. Woo-▇▇▇▇ ▇▇▇▇		Shareholder (Common)

82. ▇▇▇▇▇ ▇▇▇▇▇		Shareholder (Common)

83. ▇▇▇▇▇ ▇▇ ▇▇▇▇▇		Shareholder (Common)

84. ▇▇▇▇▇ ▇▇▇▇▇▇▇		Shareholder (Common)

85. ▇▇▇▇▇▇ ▇▇▇▇▇		Shareholder (Common)

86. Sung-▇▇▇ ▇▇▇		Shareholder (Common)

87. Samchully Pharmaceutical Co., Ltd.		Shareholder (Common)

EXHIBIT A

[Under Discussion]

Form of ▇▇▇▇▇ ▇▇▇▇▇▇▇▇ Comfort Letter

We are an independent registered public accounting firm with respect to the Company within the meaning of the Act and the applicable rules and regulations that have been adopted by the U.S. Securities and Exchange Commission (the “SEC”) and by the Public Company Accounting Oversight Board (United States) (the “PCAOB”) for a registered public accounting firm.

2)	In our opinion, the financial statements audited by us and included in the Registration Statement comply as to form, in all material respects, with the applicable accounting requirements of the Act and the Securities Exchange Act of 1934 and the related rules and regulations adopted by the SEC.

We have not audited any financial statements of the Company as of any date subsequent to September 30, 2006. Therefore, we are unable to and do not express any opinion on the unaudited balance sheets as of the interim periods included in the Registration Statement and the unaudited statements of operations and comprehensive net loss, redeemable stock and warrants, stockholders’ (deficit) equity, and cash flows for the interim periods included in the Registration Statement.

For purposes of this letter, we have read the minutes of meetings of the Board of Directors of the Company (the “Board of Directors”) through as set forth in the minute books at , officials of the Company having advised us that the minutes of all such meetings were set forth therein, except the minutes of the Board of Directors meeting held on were neither prepared nor available as of . We have carried out other procedures to April 2, 2007 as follows:

With respect to the three months ended December 31, 2006 and 2005 included in the Registration Statement, we have:

(1)

Performed the procedures specified by the PCAOB for a review of the interim financial information as described in SAS No. 100, Interim Financial Information, on the unaudited financial statements as of December 31, 2006 and 2005 and for the three months ended December 31, 2006 and 2005, respectively included in the Registration Statement.

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(2)

Inquired of certain officials of the Company who have responsibility for financial and accounting matters whether the unaudited financial statements referred to above comply as to form in all material respects with the applicable accounting requirements of the Act and the Securities Exchange Act of 1934 and the related rules and regulations adopted by the SEC.

The foregoing procedures do not constitute an audit conducted in accordance with the standards of the PCAOB. Also, they would not necessarily reveal matters of significance with respect to the comments in the following paragraph. Accordingly, we make no representations regarding the sufficiency of the foregoing procedures for your purposes.

5)	Nothing came to our attention as a result of the foregoing procedures, however, that caused us to believe that:

(i)

any material modifications should be made to the unaudited financial statements described above included in the Registration Statement, for them to be in conformity with accounting principles generally accepted in the United States of America or

(ii)

the unaudited financial statements described in 4 (i) do not comply as to form in all material respects with the applicable accounting requirements of the Act and the Securities Exchange Act of 1934 and the related rules and regulations adopted by the SEC.

Company officials have advised us that no financial statements as of any date or for any period subsequent to December 31, 2006 are available; accordingly, the procedures carried out by us with respect to changes in financial statement items after December 31, 2006, have, of necessity, been even more limited than those with respect to the periods referred to in 4 above. We have inquired of certain officials of the Company who have responsibility for financial and accounting matters whether:

(i)

There were any decreases, or changes in the composition of the Company’s stockholders’ equity (deficit) or capital stock at April 2, 2007 as compared with the December 31, 2006 amounts included in the Registration Statement

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(ii)

There were any increases at April 2, 2007, in the long-term debt as compared with the December 31, 2006 amounts included in the Registration Statement

(iii)

There were any decreases in the total assets at April 2, 2007 as compared with December 31, 2006 amounts included in the Registration Statement

(iv)

For the period from December 31, 2006 to April 2, 2007 there were any decreases, as compared with the corresponding period in the preceding year, in total revenues or in amounts of net income.

On the basis of these inquiries and our reading of the minutes as described in 4, nothing came to our attention that caused us to believe that there was any such change, increase or decrease except in all instances for changes, increases, or decreases that the Registration Statement discloses have occurred or may occur and except that during the period mentioned in 6.iv above, the Company’s

Our audit of the financial statements for the period referred to in the second paragraph of this letter comprised of audit tests and procedures deemed necessary for the purpose of expressing an opinion on such financial statements taken as a whole. For none of the periods referred to therein, or any other period, did we perform audit tests for the purpose of expressing an opinion on individual balances of accounts or summaries of selected transactions such as those enumerated below and, accordingly, we express no opinion thereon.

8)	However, for the purposes of this letter, we have also read the items identified by you on the attached copy of the Registration Statement and have performed the following procedures, which were applied as indicated with respect to the symbols explained below:

Compared the amount for the period indicated with the corresponding amount in the financial statements included in the Registration Statement of the Company and found them to be in agreement.

Compared the amount for the period indicated with the corresponding amount in the Company’s general ledger and found them to be in agreement.

Compared the amount for the period indicated to a report or schedule prepared by the Company and found them to be in agreement. Proved the arithmetic accuracy of the report or schedule.

A-3

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Compared the amount for the period indicated to a report or schedule prepared by the Company and found them to be in agreement. Proved the arithmetic accuracy of the report or schedule and compared the amount in such report or schedule to corresponding amounts in the general ledger of the Company and found them to be in agreement.

Proved the arithmetic accuracy (percentage or amount or ratio) based on amounts for the period indicated included in the applicable financial statements included in this Registration Statement, or a report or schedule prepared by the Company and found them to be in agreement.

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Proved the arithmetic accuracy (percentage or amount or ratio) based on amounts derived from the audited financial statements as of and for the year ended September 30, 2006 audited by ▇▇▇▇▇ ▇▇▇▇▇▇▇▇ LLP and as of and for the nine month period ended September 30, 2005 audited by Deloitte & Touche LLP included in this Registration Statement.

It should be understood that we make no representation regarding questions of legal interpretation or regarding the sufficiency for your purposes of the procedures enumerated in the preceding paragraph; also, such procedures would not necessarily reveal any material misstatement of the amounts or percentages listed above. Further, we have addressed ourselves solely to the foregoing data as set forth in the Registration Statement and make no representation regarding the adequacy of disclosure or regarding whether any material facts have been omitted.

10)

This letter is solely for the information of the addressees and to assist the underwriters in conducting and documenting their investigation of the affairs of the Company in connection with the offering of the securities covered by the Registration Statement, and it is not to be used, circulated, quoted or otherwise referred to within or without the underwriters group for any purpose, including but not limited to the registration, purchase or sale of securities, nor is it to be filed with or referred to in whole or in part in the Registration Statement or any other document, except that reference may be made to it in the underwriting agreement or in any list of closing documents pertaining to the offering of the securities covered by the Registration Statement.

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EXHIBIT B

Form Of Deloitte & Touche Comfort Letter

1. As of May 5, 2006 (January 4, 2007 as to the effect of the restatement discussed in Note 15, and April [ ], 2007 as to the effect of the reverse stock split, discussed in Note 16, to the consolidated financial statements) and during the period covered by the consolidated financial statements on which we reported, we were an independent registered public accounting firm with respect to the Company within the meaning of the Act and the applicable rules and regulations thereunder adopted by the Securities and Exchange Commission (“SEC”) and the Public Company Accounting Oversight Board (United States) (“PCAOB”).

2. In our opinion, the consolidated financial statements audited by us and included in the registration statement comply as to form in all material respects with the applicable accounting requirements of the Act and the related rules and regulations adopted by the SEC.

3. We have not audited any financial statements of the Company as of any date or for any period subsequent to September 30, 2005; although we have conducted an audit for the nine months ended September 30, 2005, the purpose (and therefore the scope) of the audit was to enable us to express our opinion on the consolidated financial statements as of September 30, 2005, and for the nine months then ended, but not on the financial statements for any interim period within that year. Therefore, we are unable to and do not express any opinion on the unaudited consolidated statement of operations and comprehensive net (loss) profit and consolidated statement of cash flows for the three month period ended December 31, 2005, included in the registration statement, or on the financial position, results of operations, or cash flows as of any date or for any period subsequent to September 30, 2005.

4. This letter is solely for the information of the addressees and to assist the underwriters in conducting and documenting their investigation of the affairs of the Company in connection with the offering of the securities covered by the registration statement, and it is not to be used, circulated, quoted, or otherwise referred to within or without the underwriting group for any other purpose, including but not limited to the registration, purchase, or sale of securities, nor is it to be filed with or referred to in whole or in part in the registration statement or any other document, except that reference may be made to it in the underwriting agreement or in any list of closing documents pertaining to the offering of the securities covered by the registration statement.

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EXHIBIT C

Form of Opinion of Counsel for the Company

The final opinion in draft form should be attached as Exhibit B-1 at the time this Agreement is executed.

Opinion of Shearman & Sterling LLP, counsel for the Company to be delivered pursuant to Section 5(d) of the Underwriting Agreement.

References to the Prospectus in this Exhibit B include any supplements thereto at the Closing Date.

(i) The Company is a corporation validly existing and in good standing under the law of the State of Delaware with corporate power and authority under such law to conduct its business as described in the Prospectus.

(ii) The Company (a) has the corporate power to execute, deliver and perform the Underwriting Agreement and (b) has taken all corporate action necessary to authorize the execution, delivery and performance of the Underwriting Agreement.

(iii) The Underwriting Agreement has been duly executed and delivered by the Company.

(iv) The Shares have been duly authorized by the Company and, when issued and delivered as provided in the Underwriting Agreement, the Shares will be validly issued, fully paid and nonassessable, and the issuance of such Shares will not be subject to preemptive rights pursuant to the General Corporation Law of the State of Delaware, the certificate of incorporation or by-laws of the Company.

(v) The statements in each of the Disclosure Package and the Prospectus under the caption “Description of Capital Stock”, insofar as such statements constitute summaries of documents referred to therein, fairly summarize in all material respects the documents referred to therein. The statements in each of the Disclosure Package and the Prospectus under the caption “Certain U.S. Federal Income Tax Considerations for Non-U.S. Holders”, insofar as such statements constitute summaries of legal matters referred to therein, fairly summarize in all material respects, the legal matters referred to therein.

(vi) No authorization, approval or other action by, and no notice to or filing with, any United States federal or New York governmental authority or regulatory body, is required for the due execution, delivery or performance of the Underwriting Agreement and the issuance of the Shares, except as have been obtained and are in full force and effect under the Securities Act, or as may be required under the securities or blue sky laws of any jurisdiction in the United States in connection with the sale of the Shares.

(vii) The execution and delivery by the Company of the Underwriting Agreement do not, and the performance by the Company of its obligations thereunder (other than performance by the Company of its obligations under the indemnification section of the Underwriting

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Agreement, as to which no opinion need be rendered) will not (a) result in a violation of the Company’s certificate of incorporation or by-laws; (b) result in a violation of Generally Applicable Law, or any order, writ, judgment, injunction, decree, determination or award listed in Schedule A to such opinion, or (c) result in a breach of, a default under or the acceleration of (or entitle any party to accelerate) the maturity of any obligation of the Company under, or result in require the creation of any lien upon or security interest in any property of the Company pursuant to the terms of, any agreement or document listed in Schedule A to such opinion.

(viii) The Company is not required to register as an investment company under the Investment Company Act of 1940, as amended.

In addition, such counsel shall state that they have reviewed and participated in discussions concerning the preparation of the Registration Statement, the General Disclosure Package and the Prospectus with certain officers or employees of the Company, with its auditors, with you and your and representatives. The limitations inherent in the independent verification of factual matters and in the role of outside counsel are such, however, that such counsel cannot and does not assume any responsibility for the accuracy, completeness or fairness of the statements made in the Registration Statement, the General Disclosure Package or the Prospectus, except as set forth in paragraph vii of such opinion addressed to you, dated the date hereof.

Such counsel shall also state that on , 2007, a member of the staff of the Commission informed such counsel orally that no stop order suspending the effectiveness of the Registration Statement has been issued under the Securities Act. To the knowledge of such counsel, no proceedings for that purpose have been initiated or are pending or threatened by the Commission.

Such counsel also advises you that, subject to the limitations set forth in the preceding paragraph, on the basis of the information such counsel gained in the course of performing the services referred to above, each of the Registration Statement and the Prospectus (other than the financial statements and other financial or statistical data included therein or omitted therefrom, as to which such counsel expresses no opinion) appears on its face to be appropriately responsive in all material respects to the requirements of the Securities Act and the applicable rules and regulations of the Commission thereunder, and no facts came to such counsel’s attention which gave such counsel reason believe that (i) the Registration Statement (other than the financial statements and other financial or statistical data derived therefrom contained therein or omitted therefrom, as to which such counsel has not been requested to comment), at the time it became effective, contained an untrue statement of a material fact or omitted to state a material fact required to be stated therein or necessary in order to make the statements therein not misleading; (ii) the General Disclosure Package (other than the financial statements and other financial or statistical data contained therein or omitted therefrom, as to which such counsel has not been requested to comment), at the Applicable Time or on the date of such opinion, contained or contains an untrue statement of a material fact or omitted to state a material fact required to be stated therein or necessary in order to make the statements therein, in the light of circumstances under which they were made, not misleading, or (iii) the Prospectus (other than the financial

C-2

statements and other financial or statistical data contained therein or omitted therefrom, as to which such counsel has not been requested to comment), as of its date or the date of such opinion, contained or contains an untrue statement of a material fact or omitted or omits to state a material fact necessary in order to make the statements therein, in the light of the circumstances under which they were made, not misleading.

In rendering such opinion, such counsel may rely (A) as to matters involving the application of laws of any jurisdiction other than the General Corporation Law of the State of Delaware, the New York Corporation Law or the federal law of the United States, to the extent they deem proper and specified in such opinion, upon the opinion (which shall be dated the Closing Date or any Subsequent Closing Date, as the case may be, shall be reasonably satisfactory in form and substance to the Underwriters, shall expressly state that the Underwriters may rely on such opinion as if it were addressed to them and shall be furnished to the Representatives) of other counsel of good standing whom they believe to be reliable and who are reasonably satisfactory to counsel for the Underwriters; and (B) as to matters of fact, to the extent they deem proper, on certificates of responsible officers of the Company and public officials.

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EXHIBIT D

Form of Opinion of In-house Counsel for the Company

The final opinion in draft form should be attached as Exhibit B-2 at the time this Agreement is executed.

Opinion of in-house counsel for the Company to be delivered pursuant to Section 5(d) of the Underwriting Agreement.

References to the Prospectus in this Exhibit B-2 include any supplements thereto at the Closing Date.

(i) The Company’s authorized equity capitalization is as set forth in the Prospectus. The authorized, issued and outstanding capital stock of the Company (including the Common Stock) conform to the descriptions thereof set forth in the Prospectus. All of the outstanding shares of Common Stock have been duly authorized and validly issued, are fully paid and nonassessable.

(ii) To the best knowledge of such counsel, there are no legal or governmental actions, suits or proceedings pending or threatened which are required to be disclosed in the Registration Statement, other than those disclosed therein or in the Disclosure Package.

(iii) Except as disclosed in the Prospectus, to the best knowledge of such counsel, there are no persons with registration or other similar rights to have any equity or debt securities registered for sale under the Registration Statement or included in the offering contemplated by the Underwriting Agreement, except for such rights as have been duly waived.

(iv) The Company is duly qualified as a foreign corporation to transact business and is in good standing in each jurisdiction in which such qualification is required, whether by reason of the ownership or leasing of property or the conduct of business, except for such jurisdictions where the failure to so qualify or to be in good standing would not, individually or in the aggregate, have a Material Adverse Effect.

(v) The statements in each of the Disclosure Package and the Prospectus under the headings “Description of Capital Stock” and “Certain Relationships and Related Party Transactions and in Items 14 and 15 of the Registration Statement, insofar as such statements summarize legal matters, agreements, documents or proceedings discussed therein, are accurate and fair summaries of such legal matters, agreements, documents or proceedings.

(vi) To the best knowledge of such counsel, the Company (A) is not in violation of any statute, law, rule, judgment, regulation, order or decree applicable to the Company of any court, regulatory body, administrative agency, governmental body, arbitrator or other authority having jurisdiction over the Company or any of its properties or (B) is not in Default in the performance or observance of any obligation, agreement, covenant or condition contained in any material Existing Instrument, except with respect to this clause (B) only, for such Defaults as would not, individually or in the aggregate, have a Material Adverse Effect.

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(vii) The Company possesses such valid and current licenses, certificates, authorizations or permits issued by the appropriate state, federal or foreign regulatory agencies or bodies necessary to conduct their respective businesses, and the Company has not received any notice of proceedings relating to the revocation or modification of, or non-compliance with, any such license, certificate, authorization or permit which, singly or in the aggregate, if the subject of an unfavorable decision, ruling or finding, could have a Material Adverse Effect.

(viii) To the best knowledge of such counsel, the Company is not in violation of its charter or by-laws.

(ix) Except as disclosed in the Disclosure Package and the Prospectus, to such counsel’s knowledge, the Company has not received any notice of infringement of, and to the best of such counsel’s knowledge, there is no infringement of Intellectual Property Rights of others, which infringement or conflict, if the subject of an unfavorable decision, would, singly or in the aggregate, have a Material Adverse Effect. The Company is not a party to or bound by any options, licenses or agreements with respect to the Intellectual Property Rights of any other person or entity that are required to be set forth in the Prospectus and are not described in all material respects. To such counsel’s knowledge, none of the technology employed by the Company has been obtained or is being used by the Company in violation of any contractual obligation binding on the Company or any of its officers, directors or employees or otherwise in violation of the rights of any persons.

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EXHIBIT E

Form of Opinion of Patent Counsel for the Company

The final opinion in draft form should be attached as Exhibit C at the time this Agreement is executed.

Opinion of Merchant & ▇▇▇▇▇ P.C., patent counsel for the Company to be delivered pursuant to Section 5(d) of the Underwriting Agreement.

(i) Nothing has come to our attention causing us to believe that the statements relating to patents and patent applications owned or licensed by the Company (the “Company Patents”) of which we are aware and for which we are responsible, or relating to patents or other intellectual property rights owned by third parties, included in the Disclosure Package and the Prospectus under the headings “Risk Factors – Risks Related to Our Intellectual Property” and “Business – Intellectual Property” contain any untrue statement of material fact or fail to state any material fact necessary to make the statements therein not misleading.

(ii) To the best of our knowledge and reasonable belief, the Company owns or otherwise possesses sufficient rights under all material Intellectual Property of which we are aware, that is currently employed by the Company in connection with the business now operated by it, or that is necessary for the manufacture, use or sale of its presently proposed products as described in the Disclosure Package and the Prospectus.

(iii) To the best of our knowledge, the Company has not received any communication or notice alleging any act of infringement of any third party patents by the Company.

(iv) To the best of our knowledge and reasonable belief, the claims of all issued, unexpired U.S. Company Patents of which we are aware and for which we are responsible, are valid and enforceable under the U.S. patent laws.

(v) To the best of our knowledge, no interference, reexamination, or other judicial or administrative proceeding pertaining to the validity, enforceability, or scope of the Company Patents of which we are aware and for which we are responsible, has been threatened or declared.

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EXHIBIT F

Form of Opinion of

Regulatory Counsel for the Company

This letter is furnished to you pursuant to Section 5(d) of the Underwriting Agreement, dated April , 2007 (the “Underwriting Agreement”) among Pharmasset, Inc., a Delaware corporation (the “Company”), and Banc of America Securities LLC and UBS Securities LLC, as Representatives of the several underwriters named in Schedule A of the Underwriting Agreement (the “Underwriters”), relating to the issuance and sale by the Company of [ ] shares of common stock, $0.001 par value per share, of the Company pursuant to the terms of the Underwriting Agreement, and, at the option of the Underwriters, up to an additional [ ] shares of Common Stock of the Company (together, the “Shares”).

This firm has acted in the limited role of regulatory counsel to the Company in the U.S. Food and Drug Administration (“FDA”) area only. In such capacity, we have reviewed certain information under the following captions:

•

“Risks Related to Our Business—Risks Related to Drug Discovery, Development and Commercialization—We are subject to significant regulatory requirements, which could delay, prevent or limit our ability to market our product candidates, including clevudine, Racivir, R7128 and DFC;”

•

“Risks Related to Our Business—Risks Related to Drug Discovery, Development and Commercialization—Our product candidates must undergo rigorous clinical trials, the results of which are uncertain and could substantially delay or prevent us from bringing drugs to market;”

•

“Risks Related to Our Business—Risks Related to Drug Discovery, Development and Commercialization—Delays in clinical trials could result in increased costs to us and delay our ability to obtain regulatory approval and commercialize our product candidates;”

•

“Risks Related to Our Business—Risks Related to Drug Discovery, Development and Commercialization—Failure to recruit and enroll patients for clinical trials may cause the development of our product candidates to be delayed;”

•

“Risks Related to Our Business—Risks Related to Drug Discovery, Development and Commercialization—Our product candidates may have undesirable side effects when used alone or in combination with other products that prevent their regulatory approval or limit their use if approved;”

•

“Risks Related to Our Business—Risks Related to Drug Discovery, Development and Commercialization—Even if we obtain regulatory approvals, our marketed drugs will be subject to ongoing regulatory review. If we fail to comply with continuing U.S. and foreign regulations, we could lose our marketing approvals and our business would be seriously harmed;”

•

“Risks Related to Our Business—Risks Related to Drug Discovery, Development and Commercialization—We and our collaborators will be subject to stringent federal, state and foreign regulation of sales and marketing of any approved drug candidate and a failure to comply with these regulations could result in substantial penalties;”

•

“Risks Related to Our Business—Risks Related to Our Dependence on Third Parties—We and our collaborators depend on third parties to conduct our clinical trials, which may result in costs and delays that prevent us from obtaining regulatory approval or successfully commercializing our product candidates;”

F-1

•

“Risks Related to Our Business—Risks Related to Our Dependence on Third Parties—If parties on whom we rely to manufacture our products or product candidates do not manufacture the active pharmaceutical ingredients or finished products of satisfactory quality, in a timely manner, in sufficient quantities or at an acceptable cost, clinical development and commercialization of our product candidates could be delayed;” and

•

“Business—Government Regulation—Pharmaceutical Regulation in the United States.”

(collectively, the “FDA Regulatory Sections”) in the Company’s final Prospectus dated April , 2007 (the “Prospectus”), forming a part of the Company’s Registration Statement on Form S-1, as amended (Registration No. 333-133907).

We have not been retained or engaged by the Company to perform, nor have we performed, any review of any other information in the Prospectus. Additionally, we have not been retained or engaged to provide advice in respect of United States securities laws or the rules or regulations of the Commission thereunder (the “Rules”), nor have we been retained or engaged by the Company to provide advice as to whether any information or any statement, opinion or other writing is required under the United States securities laws or the Rules to be filed with or submitted to, or incorporated into any document that will be filed with or submitted to, the Commission, and the matters addressed herein should not be construed as such advice. Terms used herein that are defined in the Underwriting Agreement shall have the respective meanings set forth in the Underwriting Agreement, unless otherwise defined herein.

For purposes of our opinion, we have examined copies of the following (the “Documents”):

An executed copy of the Underwriting Agreement.

The information contained in the FDA Regulatory Sections.

A certificate of certain officers of the Company, dated the date hereof as to certain facts relating to the Company.

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In our examination of the Underwriting Agreement and the other Documents, we have assumed the genuineness of all signatures, the legal capacity of all natural persons, the accuracy and completeness of all of the Documents, the authenticity of all originals of the Documents and the conformity to authentic originals of all of the Documents submitted to us as copies (including telecopies). Further, for purposes of our opinion, we have not independently verified nor do we take any responsibility for nor are we addressing in any way any statements of fact, any statements concerning state or foreign law, any legal conclusions or any statements of belief attributable to the Company or whether or not the Company is in compliance with applicable FDA requirements. Our opinion is given in the context of the foregoing.

This letter is based as to matters of law solely on the Federal Food, Drug, and Cosmetic Act, as amended (the “FDC Act”), and the regulations promulgated thereunder.

Based upon, subject to and limited by the assumptions, qualifications, exceptions, and limitations set forth in this opinion letter, we are of the opinion that the statements in the FDA Regulatory Sections, insofar as such statements purport to summarize applicable provisions of the FDC Act and the regulations promulgated thereunder, are accurate summaries in all material respects of the provisions purported to be summarized under such captions in the Prospectus.

Nothing herein shall be construed to cause us to be considered “experts” within the meaning of Section 11 of the Securities Act of 1933, as amended.

We express no opinion in this letter as to any other laws and regulations not specifically identified above as being covered hereby (and in particular, we express no opinion as to any effect that such other laws and regulations may have on the opinions expressed herein). We express no opinion in this letter as to federal or state securities, antitrust, unfair competition, banking, or tax laws or regulations, foreign laws or regulations, or laws or regulations of any political subdivision below the state level.

We assume no obligation to advise you of any changes in the foregoing subsequent to the delivery of this letter. This letter has been prepared solely for your use in connection with the Closing under the Underwriting Agreement on the date hereof, and it should not be quoted in whole or in part or otherwise be referred to, and should not be filed with or furnished to any governmental agency or other person or entity, without the prior written consent of this firm. In no event may this letter or any other communication or document referring to the contents hereof or any other advice we have given to the Company be submitted to or filed with the Commission without our prior written consent.

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EXHIBIT G

Form of Lock-Up Letter

, ▇▇▇▇

▇▇▇▇ ▇▇ ▇▇▇▇▇▇▇ SECURITIES LLC

▇ ▇▇▇▇ ▇▇^▇▇ ▇▇▇▇▇▇

▇▇▇ ▇▇▇▇, ▇▇ ▇▇▇▇▇

UBS SECURITIES LLC

▇▇▇ ▇▇▇▇ ▇▇▇▇▇▇

▇▇▇ ▇▇▇▇, ▇▇ ▇▇▇▇▇

As Representatives of the Several Underwriters

Re:	Pharmasset, Inc. (the “Company”)

Ladies and Gentlemen:

The undersigned is an owner of record or beneficially of certain shares of Common Stock of the Company (“Common Stock”) or securities convertible into or exchangeable or exercisable for Common Stock. The Company proposes to carry out a public offering of Common Stock (the “Offering”) for which you will act as a representative of the underwriters. The undersigned recognizes that the Offering will be of benefit to the undersigned and will benefit the Company. The undersigned acknowledges that you and the other underwriters are relying on the representations and agreements of the undersigned contained in this letter in carrying out the Offering and in entering into underwriting arrangements with the Company with respect to the Offering.

In consideration of the foregoing, the undersigned hereby agrees that the undersigned will not, (and will cause any spouse or immediate family member of the spouse or the undersigned living in the undersigned’s household not to), without the prior written consent of Banc of America Securities LLC (which consent may be withheld in its sole discretion), directly or indirectly, sell, offer, contract or grant any option to sell (including without limitation any short sale), pledge, transfer, establish an open “put equivalent position” or liquidate or decrease a “call equivalent position” within the meaning of Rule 16a-1(h) under the Securities Exchange Act of 1934, as amended, or otherwise dispose of or transfer (or enter into any transaction which is designed to, or might reasonably be expected to, result in the disposition of) including the filing (or participation in the filing of) of a registration statement with the Securities and Exchange Commission in respect of, any shares of Common Stock, options or warrants to acquire shares of Common Stock, or securities exchangeable or exercisable for or convertible into shares of Common Stock currently or

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hereafter owned either of record or beneficially (as defined in Rule 13d-3 under the Securities Exchange Act of 1934, as amended) by the undersigned (or such spouse or family member), or publicly announce an intention to do any of the foregoing, for a period commencing on the date of the first filing of the registration statement used in connection with the Offering and continuing through the close of trading on the date 180 days after the date of the Prospectus (as defined in the Underwriting Agreement) (the “Lock-Up Period”). In addition, the undersigned agrees that, without the prior written consent of Banc of America Securities LLC, it will not, during the Lock-Up Period, make any demand for or exercise any right with respect to, the registration of any shares of Common Stock or any security convertible into or exercisable or exchangeable for Common Stock.

If (i) the Company issues an earnings release or material news, or a material event relating to the Company occurs, during the last 17 days of the Lock-Up Period, or (ii) prior to the expiration of the Lock-Up Period, the Company announces that it will release earnings results during the 16-day period beginning on the last day of the Lock-Up Period, the restrictions imposed by this agreement shall continue to apply until the expiration of the 18-day period beginning on the issuance of the earnings release or the occurrence of the material news or material event, unless Banc of America Securities LLC waives, in writing, such extension. The undersigned hereby acknowledges that the Company has agreed in the Underwriting Agreement to provide written notice of any event that would result in an extension of the Lock-Up Period pursuant to the previous sentence to the undersigned (in accordance with Section 14 of the Underwriting Agreement) and agrees that any such notice properly delivered will be deemed to have been given to, and received by, the undersigned. The undersigned hereby further agrees that, prior to engaging in any transaction or taking any other action that is subject to the terms of this letter agreement during the period from the date of this letter agreement to and including the 34th day following the expiration of the initial Lock-Up Period, it will give notice thereof to the Company and will not consummate such transaction or take any such action unless it has received written confirmation from the Company that the Lock-Up Period (as such may have been extended pursuant to the previous paragraph) has expired.

The foregoing two paragraphs shall not apply to (i) any shares acquired from Banc of America Securities LLC, UBS Securities LLC or any other underwriters as part of the Offering in connection with the directed share program, (ii) transactions relating to shares of Common Stock or other securities acquired in open market transactions after completion of the Offering or (iii) the transfer of any or all of the shares of Common Stock owned by the undersigned, either during his lifetime or on death, by gift, will or intestate succession to the immediate family of the undersigned or to a trust the beneficiaries of which are exclusively the undersigned and/or a member or members of his immediate family; provided, however, that in any such case it shall be a condition to such transfer that the transferee executes and delivers to Banc of America Securities LLC and UBS Securities LLC an agreement stating that the transferee is receiving and holding the Common Stock subject to the provisions of this letter agreement, and there shall be no further transfer of such Common Stock except in accordance with this letter.

The undersigned also agrees and consents to the entry of stop transfer instructions with the Company’s transfer agent and registrar against the transfer of shares of

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Common Stock or securities convertible into or exchangeable or exercisable for Common Stock held by the undersigned except in compliance with the foregoing restrictions.

With respect to the Offering only, the undersigned waives any registration rights relating to registration under the Securities Act of any Common Stock owned either of record or beneficially by the undersigned, including any rights to receive notice of the Offering.

This agreement is irrevocable and will be binding on the undersigned and the respective successors, heirs, personal representatives, and assigns of the undersigned.




Printed Name of Holder

By:
		Signature


Printed Name of Person Signing (and indicate capacity of person signing if signing as custodian, trustee, or on behalf of an entity)

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Pharmasset, Inc. Common Stock UNDERWRITING AGREEMENT dated April 25, 2007 Banc of America Securities LLC UBS Securities LLC

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