Exhibit 4.11
                            CRIMSON EXPLORATION, INC.
                          REGISTRATION RIGHTS AGREEMENT
                          -----------------------------
     This Registration Rights Agreement (this "Agreement") is entered into as of
March 20, 2006, by and among Crimson Exploration, Inc., a Delaware corporation
(the "Company"), and the entities and Persons identified on the signature pages
of this Agreement (individually, a "Shareholder," and collectively, the
"Shareholders").
                                    RECITALS
                                    --------
     WHEREAS, this Agreement is made pursuant to the Agreement and Plan of
Merger (the "Merger Agreement") dated as of March 14, 2006, among the Company,
Crimson Exploration Operating, Inc., a Delaware corporation and wholly owned
subsidiary of the Company ("Crimson Sub"), Core Natural Resources, Inc, a Texas
corporation ("Target") and the Shareholders;
     WHEREAS, pursuant to the Merger Agreement, (a) Target will be merged with
and into Crimson Sub (the "Merger") and (b) the Company will issue shares of
Common Stock of the Company to the Shareholders in conversion of and exchange
for the outstanding shares of capital stock of Target then held by the
Shareholders;
     WHEREAS, pursuant to the Merger Agreement, certain of the Shareholders will
also assign certain of their overriding royalty interests in oil and gas
properties of the Target to the Company and the Company will issue additional
shares of Common Stock of the Company to such Shareholders (the "Assignment of
ORRI"); and
     WHEREAS, in connection with the Merger and the Assignment of ORRI, the
parties desire to enter into this Agreement in order to grant certain
registration rights with respect to the Common Stock issued to the Shareholders.
                                    AGREEMENT
                                    ---------
     NOW, THERFORE, in consideration of the mutual promises and covenants set
forth herein, the parties hereto agree as follows:
     Section 1.      Piggyback Registration Rights.
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            (a)      Right to Include  Registrable  Securities.  At any time the
     Company  proposes  for any reason to register any of its Common  Stock
     under the  Securities  Act,  either for its own  account or for the account
     of a securityholder  of  the  Company  exercising  demand   registration
     rights  other  than  pursuant  to  a Registration  Statement on Forms S-4
     or S-8 (or similar or successor  forms) (a "Proposed  Registration"), the
     Company shall promptly give written notice of such Proposed  Registration
     to all of the  Shareholders holding  Registrable  Securities  (which
     notice  shall be given not less than twenty (20) days before the expected
     effective date of the Company's  Registration  Statement) and shall offer
     such  Shareholders the right  to  request  inclusion  of  any of  such
     Shareholder's  Registrable  Securities  in  the  Proposed Registration. The
     rights to piggyback registration may be exercised an unlimited number of
     occasions.
                                       1
            (b)      Piggyback  Procedure.  Each  Shareholder  shall  have  ten
     (10)  days  from  the  date of  receipt  of the Company's  notice referred
     to in Section 1(a) to deliver to the Company a written  request  specifying
     the number of Registrable  Securities such Shareholder intends to sell and
     such Shareholder's  intended method of  disposition.   Any  Shareholder
     may  withdraw  such  Shareholder's  request  for  inclusion  of  such
     Shareholder's  Registrable  Securities in any Registration  Statement
     pursuant to this Section 1 by giving written  notice to the  Company of
     such  withdrawal;  provided,  however,  that the  Company  may ignore a
     notice of  withdrawal  made within  twenty-four  (24) hours of the time the
     Registration  Statement is to become  effective.  Subject to Section 1(d),
     the Company shall use its reasonable  best efforts to include in such
     Registration  Statement  all such  Registrable  Securities  so requested to
     be included  therein; provided,  however,  that the Company may at any time
     withdraw or cease  proceeding with any such Proposed Registration  if it
     withdraws  or  ceases  proceeding  with  the  registration  of all  other
     securities originally  proposed  to be  registered.  If the  Proposed
     Registration  is,  in  whole  or in  part,  an underwritten  public
     offering of  securities  of the Company,  any request  under this Section
     1(b) shall specify that the Registrable  Securities be included in the
     underwriting on the same terms and conditions as the shares, if any,
     otherwise being sold through underwriters under such registration.
            (c)      Priority  for  Piggyback  Registration.  Notwithstanding
     any other  provision  of this  Section 1, if the managing  underwriter  of
     an  underwritten  public  offering  determines  and advises the Company
     that the inclusion of all Registrable  Securities proposed to be included
     by the Participating  Shareholders in the underwritten  public offering
     would  materially and adversely  interfere with the successful  marketing
     of the Company's securities,  then the Participating  Shareholders may not
     include any Registrable Securities in excess of the  amount,  if any,  of
     Registrable  Securities  which the  managing  underwriter  of such
     underwritten  public  offering  shall  reasonably  and in good  faith
     agree in writing to include in such public  offering in addition to the
     amount of  securities to be  registered  for the Company.  The Company
     must include in such Registration Statement, as to each Participating
     Shareholder,  only a portion of the Registrable  Securities  such
     Participating  Shareholder  has requested be registered  equal to the ratio
     which such  Participating  Shareholder's  requested  Registrable
     Securities  bears to the total number of Registrable  Securities  requested
     to be included in such  Registration  Statement  by all  Participating
     Shareholders  who have  requested  that their  Registrable  Securities  be
     included  in such  Registration Statement.  Pursuant  to  the  foregoing
     provision,  the  securities  to be  included  in a  registration initiated
     by the Company shall be allocated:
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              (i)      first, to the Company;
              (ii)     second,  to  any  others  requesting  registration  of
     securities  of  the  Company  pursuant  to  demand registration rights;
              (iii)    third to persons or entities  exercising  registration
     rights under the Shareholders  Rights Agreement of the Company, dated
     February 28, 2006, as amended from time to time; and
              (iv)     fourth,  to the  Participating  Shareholders  and others
     having the right to include  securities  in such Registration Statement.
If as a result of the provisions of this Section 1(c), any Participating
Shareholder may not include all of its Registrable Securities in a registration
that such Shareholder has requested to be so included, such Participating
Shareholder may withdraw such Participating Shareholder's request to include
Registrable Securities in such Registration Statement.
     (d)      Registration Procedures. The Company shall use its best efforts to
effect the registration and sale of the Registrable Securities in accordance
with the intended method of distribution thereof as promptly as possible, and in
connection with any such request, the Company shall, as expeditiously as
possible:
              (i)      Preparation  of  Registration  Statement;  Effectiveness.
     Prepare  and file  with the SEC a  Registration Statement on any form on
     which the Company then  qualifies,  which counsel for the Company shall
     deem  appropriate  and  pursuant  to which  such  offering  may be made in
     accordance  with the intended method of distribution  thereof (except that
     the  Registration  Statement shall contain such  information  as may
     reasonably  be  requested  for  marketing  or other  purposes  by the
     managing  underwriter),  and use its best efforts to cause any registration
     required  hereunder to become  effective  as soon as  practicable  after
     the  initial  filing  thereof  and  remain effective until the securities
     are no longer Registrable Securities;
              (ii)     10b-5  Notification.  Promptly notify in writing the
      Participating  Shareholders,  the sales or placement agent, if any,
      therefor and the managing  underwriter of the securities  being sold
      pursuant to the  Registration  Statement  at any time when a prospectus
      relating  thereto is required to be delivered  under the Securities  Act
      upon discovery  that, or upon the happening of any event as a result of
      which,  any  prospectus  included in the  Registration  Statement  (or
      amendment or supplement  thereto)  contains  an untrue  statement  of a
      material  fact or omits to state any material  fact  required to be stated
      therein or necessary to make the  statements  therein not misleading  in
      light of the  circumstances  under which they were made,  and the  Company
      shall promptly  prepare a supplement or amendment to such  prospectus and
      file it with the SEC (in any event  no  later  than  ten  days  following
      notice  of the  occurrence  of such  event to each Participating
      Shareholder,  the sales or placement agent and the managing  underwriter)
      so that after  delivery of such  prospectus,  as so amended or
      supplemented,  to the purchasers of such Registrable  Securities,  such
      prospectus,  as so amended or supplemented,  shall not contain an untrue
      statement of a material  fact or omit to state any material  fact
      required to be stated therein  or  necessary  to  make  the  statements
      therein  not  misleading  in  light  of  the circumstances under which
      they were made;
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              (iii)    Notification of Stop Orders;  Suspensions of
      Qualifications  and  Exemptions.  Promptly notify in writing the
      Participating  Shareholders,  the  sales  or  placement  agent,  if any,
      therefor  and the managing  underwriter  of the  securities  being sold of
      the issuance by the SEC of (A) any stop order issued or threatened to be
      issued by the SEC or (B) any  notification  with respect to the suspension
      of the  qualification  or exemption  from  qualification  of any of the
      Registrable Securities for sale in any  jurisdiction  or the initiation or
      threatening of any proceeding for such  purpose and the Company  agrees to
      use its best efforts to (x) prevent the issuance of any such stop order,
      and in the event of such  issuance,  to obtain the withdrawal of any such
      stop order and (y)  obtain  the  withdrawal  of any order  suspending  or
      preventing  the use of any related  prospectus or suspending the
      qualification of any Registrable  Securities  included in the Registration
      Statement for sale in any jurisdiction at the earliest practicable date;
              (iv)     Amendments  and  Supplements.  Prepare  and file with the
       SEC such  amendments,  including  post-effective amendments  to  the
       Registration  Statement  as may  be  necessary  to  keep  the
       Registration Statement  continuously  effective for the  applicable  time
       period  required  hereunder and, if applicable,  cause  the  related
       prospectus  to be  supplemented  by  any  required  prospectus
       supplement,  and as so supplemented to be filed pursuant to Rule 424
       (or any similar  provisions then in force)  promulgated  under the
       Securities  Act; and comply with the  provisions  of the Securities Act
       and the Exchange Act with respect to the  disposition  of all securities
       covered by the  Registration  Statement  during such period in accordance
       with the intended  methods of disposition by the sellers thereof set
       forth in the  Registration  Statement as so amended or in such prospectus
       as so supplemented;
             (v)       Blue Sky. Use its reasonable best efforts to, prior to
       any public offering of the Registrable Securities, register or qualify
       (or seek an exemption from registration or qualifications) such
       Registrable Securities under such other securities or blue sky laws of
       such jurisdictions as any Participating Shareholder or underwriter may
       request, and to continue such qualification in effect in each such
       jurisdiction for as long as is permissible pursuant to the laws of
       such jurisdiction, or for as long as a Participating Shareholder or
       underwriter requests or until all of such Registrable Securities are
       sold, whichever is shortest, and do any and all other acts and things
       which may be reasonably necessary or advisable to enable any
       Participating Shareholder to consummate the disposition in such
       jurisdictions of the Registrable Securities; provided, however, that
       the Company shall not be required to (i) qualify generally to do
       business in any jurisdiction or to register as a broker or dealer in
       such jurisdiction where it would not otherwise be required to qualify
       but for this Section 1(d)(v), (ii) subject itself to taxation in any
       such jurisdiction, or (iii) submit to the general service of process
       in any such jurisdiction;
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             (vi)      Other Approvals. Use its reasonable best efforts to
       obtain all other approvals, consents, exemptions or authorizations from
       such governmental agencies or authorities as may be necessary to enable
       the Participating Shareholders and underwriters to consummate the
       disposition of Registrable Securities;
             (vii)     Agreements. Enter into customary agreements (including
       any underwriting agreements in customary form), and take such other
       actions as may be reasonably required in order to expedite or facilitate
       the disposition of Registrable Securities;
             (viii)    SEC Compliance, Earnings Statement. Comply with all
       applicable rules and regulations of the SEC and make available to its
       Shareholders, as soon as reasonably practicable, but no later than
       fifteen (15) months after the effective date of the Registration
       Statement, an earnings statement covering a period of twelve (12) months
       beginning after the effective date of the Registration Statement, in a
       manner which satisfies the provisions of Section 11(a) of the Securities
       Act and Rule 158 thereunder;
             (ix)      Certificates, Closing. Provide officers' certificates and
       other customary closing documents;
             (x)       NASD.  Cooperate  with  each  Participating   Shareholder
       and  each  underwriter   participating  in  the disposition of such
       Registrable  Securities and  underwriters'  counsel in connection  with
       any filings required to be made with the NASD;
             (xi)      Listing. Use its best efforts to cause all such
       Registrable Securities to be listed on each securities exchange  on which
       similar  securities  issued by the  Company  are then  listed  and if not
       so listed, to be listed on the NASD automated quotation system;
             (xii)     Transfer  Agent,  Registrar  and  CUSIP.  Provide a
       transfer  agent  and  registrar  for all  Registrable Securities
       registered pursuant hereto and a CUSIP number for all such Registrable
       Securities, in each case, no later than the effective date of such
       registration; and
             (xiii)    Best Efforts. Use its reasonable best efforts to take all
       other actions necessary to effect the registration of the Registrable
       Securities contemplated hereby.
     (e)      Seller Information. The Company may require each Participating
Shareholder as to which any registration of such Shareholder's Registrable
Securities is being effected to furnish to the Company with such information
regarding such Participating Shareholder and such Participating Shareholder's
method of distribution of such Registrable Securities as the Company may from
time to time reasonably request in writing. If a Participating Shareholder
refuses to provide the Company with any of such information on the grounds that
it is not necessary to include such information in the Registration Statement,
the Company may exclude such Participating Shareholder's Registrable Securities
from the Registration Statement if the Company provides such Participating
Shareholder with an opinion of counsel to the effect that such information
should be included in the Registration Statement and such Participating
Shareholder continues thereafter to withhold such information. The exclusion of
a Participating Shareholder's Registrable Securities shall not affect the
registration of the other Registrable Securities to be included in the
Registration Statement.
                                       5
     (f)      Notice to Discontinue. Each Participating Shareholder whose
Registrable Securities are covered by the Registration Statement filed pursuant
to this Agreement agrees that, upon receipt of written notice from the Company
of the happening of any event of the kind described in Section 1(d)(ii) or
Section 1(d)(iii), such Participating Shareholder shall forthwith discontinue
the disposition of Registrable Securities until such Participating Shareholder's
receipt of the copies of the supplemented or amended prospectus contemplated by
Section 1(d)(ii) or Section 1(d)(iii) or until it is advised in writing by the
Company that the use of the prospectus may be resumed and has received copies of
any additional or supplemental filings which are incorporated by reference into
the prospectus, and, if so directed by the Company in the case of an event
described in Section 1(d)(ii) or Section 1(d)(iii), such Participating
Shareholder shall deliver to the Company (at the Company's expense) all copies,
other than permanent file copies then in such Participating Shareholder's
possession, of the prospectus covering such Registrable Securities which is
current at the time of receipt of such notice.
     (g)      Registration Expenses. Except as otherwise provided herein, all
Registration Expenses shall be borne by the Company. All Selling Expenses
relating to Registrable Securities registered shall be borne by the
Participating Shareholders of such Registrable Securities pro rata on the basis
of the number of shares so registered.
     (h)      Indemnification.
              (i)      Indemnification  by the Company.  The Company agrees,
     notwithstanding  termination of this Agreement,  to indemnify  and  hold
     harmless  to  the  fullest  extent  permitted  by  applicable  law,  each
     Shareholder, each of its directors, officers, employees, advisors, agents
     and general or limited partners (and the directors, officers, employees,
     advisors and agents thereof), their respective Affiliates and each Person
     who controls (within the meaning of the Securities Act or the Exchange Act)
     any of such Persons, and each underwriter and each Person who controls
     (within the meaning of the Securities Act or the Exchange Act) any
     underwriter (collectively, "Shareholder Indemnified Parties") from and
     against any and all losses, claims, damages, expenses (including,
     reasonable costs of investigation and fees, disbursements and other charges
     of counsel and experts and any amounts paid in settlement effected with the
     Company's consent, which consent shall not be unreasonably withheld or
                                       6
     delayed) or other liabilities (collectively, "Losses") to which any such
     Shareholder Indemnified Party may become subject under the Securities Act,
     Exchange Act, any other federal law, any state or common law or any rule or
     regulation promulgated thereunder or otherwise, insofar as such Losses (or
     actions or proceedings, whether commenced or threatened, in respect
     thereof) are resulting from or arising out of or based upon (i) any untrue,
     or alleged untrue, statement of a material fact contained in the
     Registration Statement, prospectus or preliminary prospectus (as amended or
     supplemented) or any document incorporated by reference in any of the
     foregoing or resulting from or arising out of or based upon any omission or
     alleged omission to state therein a material fact required to be stated
     therein or necessary to make the statements therein (in the case of a
     prospectus, in light of the circumstances under which they were made), not
     misleading, or (ii) any violation by the Company of the Securities Act,
     Exchange Act, any other federal law, any state or common law or any rule or
     regulation promulgated thereunder or otherwise incident to any
     registration, qualification or compliance and in any such case, the Company
     will promptly reimburse each such Shareholder Indemnified Party for any
     legal expenses and any other Losses reasonably incurred in connection with
     investigating, preparing or defending any such claim, loss, damage,
     liability, action or investigation or proceeding (collectively, a "Claim").
     Such indemnity obligation shall remain in full force and effect regardless
     of any investigation made by or on behalf of the Shareholder Indemnified
     Parties and shall survive the transfer of Registrable Securities by such
     Shareholder Indemnified Parties.
              (ii)     Indemnification  by Shareholders.  In connection with any
     proposed  registration in which a Shareholder is participating  pursuant
     to this Agreement,  each such Shareholder  shall furnish to the Company
     in writing such information with respect to such Shareholder as the Company
     may reasonably request or as may be required by law for use in connection
     with the Registration Statement or prospectus or preliminary prospectus to
     be used in connection with such registration and each Shareholder agrees,
     severally and not jointly, to indemnify and hold harmless the Company, any
     underwriter retained by the Company and their respective directors,
     officers, partners, employees, advisors and agents, their respective
     Affiliates and each Person who controls (within the meaning of the
     Securities Act or the Exchange Act) any of such Persons to the same extent
     as the foregoing indemnity from the Company to the Shareholders as set
     forth in Section 1(h)(i) (subject to the exceptions set forth in the
     foregoing indemnity, the proviso to this sentence and applicable law), but
     only with respect to any such information furnished in writing by such
     Shareholder expressly for use therein; provided, however, that, unless such
     liability is directly caused by such Shareholder's willful or intentional
     misconduct, the liability of any such Shareholder under this Section
     1(h)(ii) shall be limited to the amount of the net proceeds received by
     such Shareholder in the offering giving rise to such liability. Such
     indemnity obligation shall remain in full force and effect regardless of
     any investigation made by or on behalf of the Shareholder Indemnified
     Parties (except as provided above) and shall survive the transfer of
     Registrable Securities by such Shareholder.
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              (iii)     Conduct of Indemnification  Proceedings.  Any person or
     entity entitled to indemnification  hereunder (the "Indemnified  Party")
     agrees to give  prompt  written  notice to the  indemnifying  party (the
     "Indemnifying Party") after the receipt by the Indemnified Party of any
     written notice of the commencement of any action, suit, proceeding or
     investigation or threat thereof made in writing for which the Indemnified
     Party intends to claim indemnification or contribution pursuant to this
     Agreement; provided, however, that, the failure so to notify the
     Indemnifying Party shall not relieve the Indemnifying Party of any
     liability that it may have to the Indemnified Party hereunder unless and to
     the extent such Indemnifying Party is materially prejudiced by such
     failure. If notice of commencement of any such action is given to the
     Indemnifying Party as above provided, the Indemnifying Party may
     participate in and, to the extent it may wish, jointly with any other
     Indemnifying Party similarly notified, to assume the defense of such action
     at its own expense, with counsel chosen by it and reasonably satisfactory
     to such Indemnified Party. The Indemnified Party may employ separate
     counsel in any such action and participate in the defense thereof, but the
     fees and expenses of such counsel shall be paid by the Indemnified Party
     unless (i) the Indemnifying Party agrees to pay the same, (ii) the
     Indemnifying Party fails to assume the defense of such action with counsel
     satisfactory to the Indemnified Party in its reasonable judgment or (iii)
     the named parties to any such action reasonably believe that the
     representation of such Indemnified Party and the Indemnifying Party by the
     same counsel would be inappropriate under applicable standards of
     professional conduct. In the case of clause (ii) above and (iii) above, the
     Indemnifying Party may not assume the defense of such action on behalf of
     such Indemnified Party. No Indemnifying Party shall be liable for any
     settlement entered into without its written consent, which consent shall
     not be unreasonably withheld. No Indemnifying Party may, without the
     written consent of the Indemnified Party, (which consent shall not be
     unreasonably withheld), effect the settlement or compromise of, or consent
     to the entry of any judgment with respect to, any pending or threatened
     Claim in respect of which indemnification or contribution may be sought
     hereunder (whether or not the Indemnified Party is an actual or potential
     party to such Claim) unless such settlement, compromise or judgment (A)
     includes an unconditional release of the Indemnified Party from all
     liability arising out of such Claim and (B) 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. The rights afforded to any Indemnified
     Party hereunder shall be in addition to any rights that such Indemnified
     Party may have at common law, by separate agreement or otherwise.
               (iv)     Contribution.  If the  indemnification  provided for in
     this Section 1(h) from the  Indemnifying  Party is unavailable or
     insufficient  to hold harmless an  Indemnified  Party in respect of any
     Losses, then the Indemnifying  Party, in lieu of indemnifying the
     Indemnified  Party,  shall contribute to the  amount  paid or  payable by
                                       8
     the  Indemnified  Party as a result of such  Losses in such proportion as
     is appropriate to reflect the relative  fault of the  Indemnifying  Party
     and the Indemnified  Party,  as well as any  other  relevant  equitable
     considerations.  The  relative faults of the  Indemnifying  Party and
     Indemnified  Party shall be determined by reference to, among other
     things,  whether any action in question,  including  any untrue or alleged
     untrue statement  of a material  fact or omission or alleged  omission to
     state a material  fact,  was made by, or relates to information  supplied
     by, such Indemnifying  Party or Indemnified Party, and the Indemnifying
     Party's and Indemnified  Party's relative  intent,  knowledge,  access to
     information and opportunity to correct or prevent such action; provided,
     however, that, unless such liability is directly caused by such
     Shareholder's willful or intentional misconduct, the liability of any such
     Shareholder under this Section 1(h)(iv) shall be limited to the amount of
     the net proceeds received by such Shareholder in the offering giving rise
     to such liability. The amount paid or payable by a party as a result of the
     Losses or other liabilities referred to above shall be deemed to include,
     subject to the limitations set forth in Sections 1(h)(i), Section 1(h)(ii),
     or Section 1(h)(iii), any legal or other fees, charges or expenses
     reasonably incurred by such party in connection with any investigation or
     proceeding.
               (v)      The  parties  hereto  agree  that it would not be just
     and  equitable  if  contribution  pursuant  to this Section  1(h)(iv) were
     determined by pro rata allocation or by any other method of allocation
     which does not take account of the equitable considerations referred to in
     the immediately preceding paragraph. No person guilty of fraudulent
     misrepresentation (within the meaning of Section 11(f) of the Securities
     Act) shall be entitled to contribution pursuant to this Section 1(h)(iv).
     (i)       Rule 144 and Rule 144A; Other Exemptions. The Company shall use
its commercially reasonable efforts to (i) file in a timely manner all reports
and other documents required to be filed by it under the Securities Act and the
Exchange Act and the rules and regulations adopted by the SEC thereunder and
(ii) take such further action as each Shareholder may reasonably request
(including providing any information necessary to comply with Rule 144), all to
the extent required from time to time to enable such Shareholder to sell
Registrable Securities without registration under the Securities Act within the
limitation of the exemptions provided by (x) Rule 144 under the Securities Act,
as such rules may be amended from time to time or (y) any other rules or
regulations now existing or hereafter adopted by the SEC. Upon the written
request of a Shareholder, the Company shall deliver to the Shareholder a written
statement as to whether it has complied with such requirements.
     (j)       Certain Limitations On Registration Rights. No Shareholder may
participate in the Registration Statement hereunder unless such Shareholder
completes and executes all questionnaires, powers of attorney, indemnities,
underwriting agreements, and other documents reasonably required under the terms
of such underwriting arrangements and agrees to sell such Shareholder's
Registrable Securities on the basis provided in any underwriting agreement
                                       9
approved by the Shareholder or Shareholders entitled hereunder to approve such
arrangements; provided, however, that no such Shareholder shall be required to
make any representations or warranties to the Company or the underwriters in
connection with any such registration other than representations and warranties
as to (i) such Shareholder's ownership of its Registrable Securities to be sold
or transferred, (ii) such Shareholder's power and authority to effect such
transfer and (iii) such matters pertaining to compliance with securities laws as
may be reasonably requested. Such Shareholders of Registrable Securities to be
sold by such underwriters may, at their option, require that any or all of the
representations and warranties by, and the other agreements on the part of the
Company to and for the benefit of such underwriters, shall also be made to and
for the benefit of such Shareholders and that any or all of the conditions
precedent to the obligations of the underwriters under the underwriting
agreement be conditions precedent to the obligations of the Shareholders.
     (k)    Restrictions on Public Sale by Shareholders. If requested by the
lead managing underwriter with respect to any firm underwriting public offering
in which Shareholders are permitted to participate hereunder, each Shareholder
of Registrable Securities agrees not to effect any public sale or distribution
of any Registrable Securities being registered or of any securities convertible
into or exchangeable or exercisable for such Registrable Securities, including a
sale pursuant to Rule 144 under the Securities Act, during a period of not more
than one hundred eighty (180) days after any firm underwriting public offering
of Common Stock of the Company, commencing on the effective date of the
Registration Statement (the "Lock-Up Period"), unless expressly authorized to do
so by the lead managing underwriter; provided, however, that if any other
Shareholder of securities of the Company is subject to a shorter period or
receives more advantageous terms relating to the Lock-Up Period, then the
Lock-Up Period shall be such shorter period and also on such more advantageous
terms. Notwithstanding the foregoing, the Shareholders shall not be required to
sign lock-up agreements unless other Persons permitted to include securities on
such Registration Statement and all of the Company's directors and executive
officers have signed substantially similar lock-up agreements with the managing
underwriters. Any such lock-up agreements signed by the Shareholders shall
contain reasonable and customary exceptions.
     (l)    Transfer of Registration Rights. The rights of a Shareholder under
this Section 1 may not be transferred or assigned in connection with a transfer
of Registrable Securities.
     (m)    Amendment. The provisions of this Section 1 may be waived or amended
by the agreement of Shareholders holding a majority of the Registrable
Securities.
     (n)    Definitions. For this Section 1:
     "Affiliate" means with respect to any Person, any other Person directly or
indirectly Controlling or Controlled by, or under direct or indirect common
Control with, such Person.
     "Claim" is defined in Section 1(h)(i).
                                       10
     "Common Stock" means shares of common stock, $0.01 par value per share, of
the Company.
     "Company" means Crimson Exploration, Inc., a Delaware corporation.
     "Control" means the possession, directly or indirectly, of the power to
direct or cause the direction of the management and policies of a Person,
whether through the ownership of voting securities, by contract or otherwise.
     "Exchange Act" means the Securities Exchange Act of 1934, as amended from
time to time.
     "Indemnified Party" is defined in Section 1(h)(iii).
     "Indemnifying Party" is defined in Section 1(h)(iii).
     "Losses" is defined in Section 1(h)(i).
     "NASD" means the National Association of Securities Dealers, Inc.
     "Participating Shareholders" means Shareholders participating, or electing
to participate, in an offering of Registrable Securities.
     "Person" means any individual, corporation, limited liability company,
limited or general partnership, joint venture, association, joint-stock company,
trust, unincorporated organization or government or any agency or political
subdivision thereof.
     "Proposed Registration" is defined in Section 1(a).
     "Registrable Securities" means any shares of Common Stock held by
Shareholder as listed as Registrable Securities on Schedule I and any shares of
Common Stock issued to a Shareholder as (or issuable upon the conversion or
exercise of any warrant, right or other security which is issued as) a dividend
on the Common Stock, including any resulting shares issued, by virtue of the
effect of antidilution provisions or combination, merger, consolidation or other
similar event; provided, however, that shares of Common Stock that are
considered to be Registrable Securities shall cease to be Registrable Securities
(i) upon the sale thereof pursuant to an effective registration statement, (ii)
upon the first anniversary of the date of the issuance of such shares or (iii)
when such securities cease to be outstanding.
     "Registration Expenses" means all expenses (other than underwriting
discounts and commissions) arising from or incident to the performance of, or
compliance with, Section 1, including, (i) SEC, stock exchange, NASD and other
registration and filing fees, (ii) all fees and expenses incurred in connection
with complying with any securities or blue sky laws (including, fees, charges
and disbursements of counsel in connection with blue sky qualifications of the
Registrable Securities), (iii) all printing, messenger and delivery expenses,
(iv) the fees, charges and disbursements of counsel to the Company and of its
independent public accountants and any other accounting and legal fees, charges
                                       11
and expenses incurred by the Company (including, any expenses arising from any
special audits or "comfort letters" required in connection with or incident to
any registration), (v) the fees, charges and disbursements of any special
experts retained by the Company in connection with any registration pursuant to
the terms of this Agreement, (vi) all internal expenses of the Company
(including, all salaries and expenses of its officers and employees performing
legal or accounting duties), (vii) the fees and expenses incurred in connection
with the listing of the Registrable Securities on any securities exchange,
over-the-counter market or Nasdaq and (viii) Securities Act liability insurance
(if the Company elects to obtain such insurance), regardless of whether the
Registration Statement filed in connection with such registration is declared
effective. "Registration Expenses" shall not include fees, charges and
disbursements of any firm of counsel to any Participating Shareholders.
     "Registration Statement" means the registration statement of the Company
filed with the SEC on the appropriate form pursuant to the Securities Act which
covers shares of Registrable Securities pursuant to the provisions of this
Agreement and all amendments and supplements to the Registration Statement,
including post-effective amendments, in each case including the prospectus
contained therein, all exhibits thereto and all materials incorporated by
reference therein.
     "SEC" or "Commission" means the United States Securities and Exchange
Commission.
     "Securities Act" means the Securities Act of 1933, as amended from time to
time.
     "Selling Expenses" means the underwriting fees, discounts, selling
commissions and stock transfer taxes applicable to all Registrable Securities
registered by the Participating Shareholders.
     "Shareholder" or "Shareholders" means (a) those Persons receiving shares of
Common Stock issued by the Company pursuant to the Merger Agreement and (b)
those Persons receiving shares of Common Stock issued by the Company pursuant to
the Assignment of ORRI, in each case, as set forth on Schedule I hereto.
     "Shareholder Indemnified Parties" is defined in Section 1(h)(i).
Section 2.        Miscellaneous.
     (a)          Notices. All notices, consents, waivers, and other
communications under this Agreement must be in writing and will be deemed to
have been duly given:
                  (i)     two days after deposit in the mail, if sent
     first-class United States mail;
                  (ii)    when delivered by hand (with written confirmation of
     receipt);
                  (iii)   when  sent by  facsimile  (with  written  confirmation
     of  receipt),  provided  that a copy is  mailed by registered mail, return
     receipt requested; or
                                       12
                  (iv)    when received by the addressee,  if sent by a
     nationally recognized overnight delivery service (receipt requested), in
     each case to the appropriate addresses and facsimile numbers set forth
     below (or to such other addresses and facsimile numbers as a party may
     designate by notice to the other parties).
     (b)    If to a Shareholder, as indicated on the signature pages to this
Agreement, with a copy to:
                              ▇▇▇▇▇▇▇▇ ▇▇▇▇▇ L.L.P.
                              ▇▇▇ ▇▇▇▇▇▇▇▇▇ ▇▇▇▇▇▇, ▇▇▇▇▇ ▇▇▇▇
                              ▇▇▇▇▇▇▇, ▇▇ ▇▇▇▇▇
     (c)    If to the Company:
                              Crimson Exploration, Inc.
                              Attn: ▇▇▇ ▇▇▇▇▇
                              ▇▇▇ ▇▇▇▇▇ ▇▇▇ ▇▇▇▇▇▇▇ ▇▇▇▇▇▇▇ ▇▇▇▇
                              ▇▇▇▇▇ ▇▇▇
                              ▇▇▇▇▇▇▇, ▇▇  ▇▇▇▇▇
     Section 3.    Waiver. The rights and remedies of the parties to this
Agreement are cumulative and not alternative. Neither the failure nor any delay
by any party in exercising any right, power, or privilege under this Agreement
or the documents referred to in this Agreement will operate as a waiver of such
right, power, or privilege, and no single or partial exercise of any such right,
power, or privilege will preclude any other or further exercise of such right,
power, or privilege or the exercise of any other right, power, or privilege.
     Section 4.    Entire Agreement; Amendment; Waiver. This Agreement, the
Merger Agreement, and Assignment of ORRI constitute the full and entire
understanding and agreement between the parties with regard to the subjects
hereof and thereof. Neither this Agreement nor any term hereof may be amended,
waived, discharged or terminated, except by a written instrument signed by the
Company and the holders of a majority of the Registrable Securities.
     Section 5.    Term of  Agreement.  This  Agreement  shall  terminate  on
the earlier of (i) the date upon which all of the shares of Registrable
Securities have been sold pursuant to an effective registration statement, (ii)
no Registrable Securities continue to be outstanding and (ii) the first
anniversary of the date hereof. Notwithstanding the foregoing, certain covenants
contained in this Agreement shall expire on the occurrence of the specific
events stated herein that relate to those particular covenants, if such events
occur sooner than an event set forth in this Section 5, and the obligations
contained in Section 1(h) shall survive the termination of this Agreement.
     Section 6.    Assignments;  Successors;  No Third-Party Rights. Except as
provided in this Agreement, no party may assign any of its rights under this
Agreement without the prior consent of the other parties. Subject to the
preceding sentence, this Agreement will apply to, be binding in all respects
upon, and inure to the benefit of the successors and permitted assigns of the
parties. Nothing expressed or referred to in this Agreement will be construed to
give any Person other than the parties to this Agreement any legal or equitable
right, remedy, or claim under or with respect to this Agreement or any provision
of this Agreement. This Agreement and all of its provisions and conditions are
for the sole and exclusive benefit of the parties to this Agreement and their
successors and assigns.
                                       13
     Section 7.    Severability. If any provision of this Agreement is held
invalid or unenforceable by any court of competent jurisdiction, the other
provisions of this Agreement will remain in full force and effect. Any provision
of this Agreement held invalid or unenforceable only in part or degree will
remain in full force and effect to the extent not held invalid or unenforceable.
     Section 8.    Section Headings; Construction. The headings of Sections in
this Agreement are provided for convenience only and will not affect its
construction or interpretation. All references to "Section" or "Sections" refer
to the corresponding Section or Sections of this Agreement. All words used in
this Agreement will be construed to be of such gender or number as the
circumstances require. Unless otherwise expressly provided, the word "including"
does not limit the preceding words or terms.
     Section 9.    Governing Law. This Agreement will be governed by the laws of
the State of Texas without regard to conflicts of laws principles.
     Section 10.   Counterparts. This Agreement may be executed in one or more
counterparts, each of which will be deemed to be an original copy of this
Agreement and all of which, when taken together, will be deemed to constitute
one and the same agreement.
                  [REMAINDER OF PAGE INTENTIONALLY LEFT BLANK]
                            [SIGNATURE PAGES FOLLOW]
                                       14
DATED: March 20, 2006.
                                                   CRIMSON EXPLORATION, INC.
                                                   a Delaware corporation
                                                   By:  /s/ E. ▇▇▇▇▇▇ ▇▇▇▇▇
                                                        ------------------------
                                                        E. ▇▇▇▇▇▇ ▇▇▇▇▇
                                                        ▇▇. Vice President & CFO
                                Signature Page 1
                                  SHAREHOLDERS:
DATED:  March 20, 2006.                        CORE NATURAL RESOURCES GP, LLC,
                                               a Texas limited liability company
                                               By:      /s/ ▇▇▇▇▇▇▇ ▇. ▇▇▇▇▇▇
                                                        ------------------------
                                                        ▇▇▇▇▇▇▇  ▇. ▇▇▇▇▇▇
                                                        Manager
Notice Address:                                ▇▇▇▇ ▇▇▇▇▇▇▇
                                               ▇▇▇▇▇ ▇▇▇
                                               ▇▇▇▇▇▇▇, ▇▇  ▇▇▇▇▇
DATED:  March 20, 2006.                        /s/ ▇▇▇▇▇▇▇ ▇. ▇▇▇▇▇▇
                                               ---------------------------------
                                               ▇▇▇▇▇▇▇ ▇. ▇▇▇▇▇▇
Notice Address:                                ▇▇▇▇▇ ▇▇▇▇▇▇▇▇▇ ▇▇▇▇
                                               ▇▇▇▇▇▇▇, ▇▇  ▇▇▇▇▇
DATED:  March 20, 2006.                        /s/ ▇▇▇▇▇▇▇ ▇. ▇▇▇▇▇▇
                                               ---------------------------------
                                               ▇▇▇▇▇▇▇ ▇. ▇▇▇▇▇▇
Notice Address:                                ▇▇▇ ▇▇▇▇▇▇▇ ▇▇▇▇▇▇
                                               ▇▇▇▇▇▇▇, ▇▇  ▇▇▇▇▇
DATED:  March 20, 2006.                         /s/ ▇▇▇▇▇▇▇ ▇. ▇▇▇▇▇
                                                --------------------------------
                                                ▇▇▇▇▇▇▇ ▇. ▇▇▇▇▇
Notice Address:                                 ▇▇▇▇▇ ▇▇▇▇▇▇▇▇▇▇▇
                                                ▇▇▇▇▇▇▇, ▇▇  ▇▇▇▇▇
DATED:  March 20, 2006.                         /s/ ▇▇▇▇▇▇▇ ▇. ▇▇▇▇▇
                                                --------------------------------
                                                ▇▇▇▇▇▇▇ ▇. ▇▇▇▇▇
Notice Address:                                 ▇▇▇ ▇▇▇▇▇▇▇▇▇▇ ▇▇▇▇, #▇▇
                                                ▇▇▇▇▇▇▇, ▇▇  ▇▇▇▇▇
                                Signature Page 2
DATED:  March 20, 2006.                         ▇▇▇▇▇▇▇, INC.,
                                                a Texas corporation
                                                By:      /s/ M.B. ▇▇▇▇▇
                                                         -----------------------
                                                Name:    M.B. ▇▇▇▇▇
                                                Title:   President
Notice Address:                                 c/o M.B. ▇▇▇▇▇
                                                ▇▇▇▇ ▇▇▇▇▇▇▇▇▇▇ ▇▇▇▇
                                                ▇▇▇▇▇▇▇, ▇▇  ▇▇▇▇▇
                                Signature Page 3
                                   SCHEDULE I
                                  SHAREHOLDERS
                                  ------------
                                    SHARES RECEIVED
                                     UNDER MERGER       SHARES RECEIVED UNDER
           NAME                      AGREEMENT           ASSIGNMENT OF ORRI
CORE NATURAL RESOURCES GP, LLC,      32,356.24                   -0-
a Texas limited liability company...
                                  2,814,993.18        ▇▇▇▇▇▇▇ Lease - 262,231
▇▇▇▇▇▇▇ ▇. ▇▇▇▇▇▇................                      Price Lease - 200,000
▇▇▇▇▇▇▇ ▇. ▇▇▇▇▇▇.................. 129,424.97                   -0-
▇▇▇▇▇▇▇ ▇. ▇▇▇▇▇................... 129,424.97                   -0-
▇▇▇▇▇▇▇ ▇. ▇▇▇▇▇.................... 16,178.12                   -0-
▇▇▇▇▇▇▇, INC.,                      113,246.85                   -0-
a Texas corporation................
                                Signature Page 4