ONE GAS, INC. SUPPLEMENTAL INDENTURE NO. 3 $300,000,000 2.00% Senior Notes due 2030

Exhibit 4.2

ONE GAS, INC.

SUPPLEMENTAL INDENTURE NO. 3

$300,000,000 2.00% Senior Notes due 2030

THIS SUPPLEMENTAL INDENTURE NO. 3, dated as of May 4, 2020 (this “Supplemental Indenture”), among ONE GAS, INC., an Oklahoma corporation (the “Company”) and U.S. BANK NATIONAL ASSOCIATION, a national banking association, as trustee (the “Trustee”).

RECITALS OF THE COMPANY:

WHEREAS, the Company has heretofore executed and delivered to the Trustee an Indenture, dated as January 27, 2014 (the “Original Indenture”) (the Original Indenture, as amended and supplemented from time to time, including without limitation pursuant to this Supplemental Indenture, being referred to herein as the “Indenture”), providing for the issuance from time to time of one or more series of Securities (as defined in the Indenture);

WHEREAS, Article Nine of the Original Indenture provides for various matters with respect to any series of Securities issued under the Indenture to be established in an indenture supplemental to the Original Indenture;

WHEREAS, Section 9.1(7) of the Original Indenture provides that the Company and the Trustee may enter into an indenture supplemental to the Original Indenture to establish the form or terms of Securities of any series as permitted by Sections 2.1 and 3.1 of the Original Indenture; and

WHEREAS, all the conditions and requirements necessary to make this Supplemental Indenture, when duly executed and delivered, a valid and binding agreement in accordance with its terms and for the purposes herein expressed, have been performed and fulfilled.

NOW THEREFORE, THIS SUPPLEMENTAL INDENTURE WITNESSETH:

For and in consideration of the premises and the issuance of the series of Securities provided for herein, the Company and the Trustee mutually covenant and agree for the equal and proportionate benefit of the respective Holders of the Securities of each such series as follows:

ARTICLE I

RELATION TO INDENTURE; DEFINITIONS; RULES OF CONSTRUCTION

SECTION 1.1 Relation to Indenture. This Supplemental Indenture constitutes an integral part of the Indenture.

SECTION 1.2 Definitions. For all purposes of this Supplemental Indenture, the following terms shall have the respective meanings set forth in this Section.

“Comparable Treasury Issue” means the United States Treasury security selected by a Quotation Agent as having a maturity comparable to the remaining term of the Notes being redeemed (assuming, for this purpose, that the Notes matured on February 15, 2030) that would be utilized, at the time of selection and in accordance with customary financial practice, in pricing new issues of corporate debt securities of comparable maturity to the remaining term of such Notes.

“Comparable Treasury Price” means with respect to any redemption date, (A) the average of the Reference Treasury Dealer Quotations for the redemption date, after excluding the highest and lowest Reference Treasury Dealer Quotations for that redemption date, or (b) if the Company obtains fewer than four Reference Treasury Dealer Quotations, the average of all the Reference Treasury Dealer Quotations obtained.

“Definitive Note” means a certificated Note that does not include the legend prescribed in Section 2.4 of the Original Indenture.

“Depository” means The Depository Trust Company, its nominees and their respective successors.

“Global Notes” means one or more Securities evidencing all or part of the Securities to be issued as Book-Entry Securities, issued to the Depositary in accordance with Section 3.1 of the Original Indenture and bearing the legend prescribed in Section 2.4 of the Original Indenture.

“Notes” shall have the meaning set forth in Section 2.1.

“Notes Custodian” means the custodian with respect to the Global Notes (as appointed by the Depository) or an successor person thereto, who will initially be the Trustee.

“Participant” means members of, or participants in, the Depository.

“Quotation Agent” means one of the Reference Treasury Dealers appointed by the Company.

“Reference Treasury Dealer” means each of (1) BofA Securities, Inc. and Mizuho Securities USA LLC, or their respective affiliates or successors; provided, however, that if any of the foregoing or their affiliates or successors shall cease to be a primary U.S. Government securities dealer in the United States, the Company will appoint another primary U.S. Government securities dealer as a substitute, (2) one primary U.S. Government securities dealer selected by U.S. Bancorp Investments, Inc. and (3) any other U.S. Government securities dealers selected by the Company.

“Reference Treasury Dealer Quotations” means, for each Reference Treasury Dealer and any redemption date, the average, as determined by the Company, of the bid and ask prices for the Comparable Treasury Issue (expressed in each case as a percentage of its principal amount) quoted in writing to the Trustee by the Reference Treasury Dealer at 5:00 p.m. New York City time on the third business day preceding the redemption date for the Notes being redeemed.

“Treasury Rate” means, for any redemption date, the rate per annum equal to the semi-annual equivalent yield to maturity of the Comparable Treasury Issue, assuming a price for the Comparable Treasury Issue (expressed as a percentage of its principal amount) equal to the Comparable Treasury Price for the redemption date.

SECTION 1.3 Rules of Construction. For all purposes of this Supplemental Indenture:

ARTICLE II

THE SECURITIES

SECTION 2.1 Title of the Notes. There shall be a series of Securities designated the 2.00% Senior Notes due 2030 (the “Notes”).

SECTION 2.2 Initial Principal Amount. The Notes will be initially issued in an aggregate principal amount of $300,000,000.

SECTION 2.3 Form and Dating.

(a) General. The Notes and the Trustee’s certificate of authentication shall be substantially in the form of Exhibit A hereto. The Notes may have notations, legends or endorsements required by law, stock exchange rule or usage. Each Note shall be dated the date of its authentication. The Notes shall be in denominations of $2,000 and integral multiples of $1,000 in excess thereof.

The terms and provisions contained in the Notes shall constitute, and are hereby expressly made, a part of this Supplemental Indenture, and the Company and the Trustee, by their execution and delivery of this Supplemental Indenture, expressly agree to such terms and provisions and to be bound thereby. However, to the extent any provision of any Note conflicts with the express provisions of this Supplemental Indenture, the provisions of this Supplemental Indenture shall govern and be controlling.

The Company hereby designates The Depository Trust Company as the initial depository for the Global Notes.

(b) Global Notes. The Notes shall initially be issuable in whole or in part in the form of one or more Global Notes. Such Global Notes (i) shall be deposited with, or on behalf of, the Depository, which shall act as depository with respect to the Notes, (ii) shall bear the legend prescribed by Section 2.4 of the Original Indenture, (iii) may be exchanged in whole or in part upon the terms and subject to the conditions provided in Section 3.5 of the Original Indenture and (iv) shall otherwise be subject to the applicable provisions of the Indenture.

(c) Book-Entry Provisions. This Section 2.3(c) shall apply only to a Global Note deposited with or on behalf of the Depository. The Company shall execute and the Trustee shall, in accordance with this Section 2.3(c) and pursuant to an order of the Company, authenticate and deliver initially one or more Global Notes that (a) shall be registered in the name of the Depository for such Global Note or Global Notes or the nominee of such Depository and (b) shall be delivered by the Trustee to such Depository or pursuant to such Depository’s instructions or held by the Trustee as Notes Custodian.

Participants shall have no rights under the Indenture with respect to any Global Note held on their behalf by the Depository or by the Trustee as Notes Custodian or under such Global Note, and the Depository may be treated by the Company, the Trustee and any agent of the Company or the Trustee as the absolute owner of such Global Note for all purposes whatsoever. Notwithstanding the foregoing, nothing herein shall prevent the Company, the Trustee or any agent of the Company or the Trustee from giving effect to any written certification, proxy or other authorization furnished by the Depository or impair, as between the Depository and its Participants, the operation of customary practices of such Depository governing the exercise of the rights of a holder of a beneficial interest in any Global Note.

(d) Definitive Notes. Except as provided in Section 2.4, owners of beneficial interests in Global Notes will not be entitled to receive physical delivery of certificated Notes.

(e) Cancellation of Global Note. At such time as all beneficial interests in a Global Note have either been exchanged for Definitive Notes, transferred, redeemed, repurchased or canceled, such Global Note shall be returned by the Depository to the Trustee for cancellation or retained and canceled by the Trustee. At any time prior to such cancellation, if any beneficial interest in a Global Note is exchanged for Definitive Notes, transferred in exchange for an interest in another Global Note, redeemed, repurchased or canceled, the principal amount of Notes represented by such Global Note shall be reduced and an adjustment shall be made on the books and records of the Trustee (if it is then the Notes Custodian for such Global Note) with respect to such Global Note, by the Trustee or the Notes Custodian, to reflect such reduction.

SECTION 2.4 Definitive Notes.

(a) A Global Note deposited with the Depository or with the Trustee as Notes Custodian pursuant to Section 2.3 shall be transferred to the beneficial owners thereof in the form of Definitive Notes in an aggregate principal amount equal to the principal amount of such Global Note, in exchange for such Global Note in the event (i) the Depository (A) notifies the Company that the Depository is no longer willing or able to act as a depositary or clearing system for the Notes or (B) ceases to be a “clearing agency” registered under the Securities Exchange Act of 1934, as amended, and, in either event, a successor depositary or clearing system is not appointed by the Company within 90 days of such notice or cessation, (ii) the Company, in its sole discretion, notifies the Trustee in writing that it elects to cause the issuance of Definitive Notes under the Indenture, or (iii) upon the occurrence and continuation of an Event of Default and the Depository notifies the Trustee of its decision to exchange the Global Note for Definitive Notes.

(b) Any Global Note that is transferable to the beneficial owners thereof pursuant to this Section 2.4 shall be surrendered by the Depository to the Trustee, to be so transferred, in whole or from time to time in part, without charge, and upon Company Order the Trustee shall authenticate and deliver, upon such transfer of each portion of such Global Note, an equal aggregate principal amount of Definitive Notes of authorized denominations. Any portion of a Global Note transferred pursuant to this Section 2.4 shall be executed, authenticated and delivered only in denominations of $2,000 of principal amount and any integral multiple of $1,000 in excess thereof and registered in such names as the Depository shall direct.

(c) The registered Holder of a Global Note may grant proxies and otherwise authorize any Person, including Participants and Persons that may hold interests through Participants, to take any action which a Holder is entitled to take under the Indenture or the Notes.

(d) In the event of the occurrence of any of the events specified in Section 2.4(a)(i), (ii) or (iii), the Company will promptly make available to the Trustee a reasonable supply of Definitive Notes in fully registered form without interest coupons.

SECTION 2.5 Stated Maturity. The Stated Maturity of the Notes shall be May 15, 2030.

SECTION 2.6 Interest and Interest Rate. The rate at which the Notes shall bear interest, the date or dates from which such interest shall accrue, the interest payment dates on which any such interest shall be payable and the regular record date for any interest payable on any interest payment date, in each case, shall be as set forth in the form of Note set forth as Exhibit A hereto.

SECTION 2.7 Optional Redemption. At its option, the Company may redeem the Notes, in whole or in part, at any time or from time to time, at the applicable redemption price determined as set forth in the form of Note attached hereto as Exhibit A, in accordance with the terms set forth therein and in accordance with Article XI of the Original Indenture.

ARTICLE III

MISCELLANEOUS PROVISIONS

SECTION 3.1 Ratification. The Indenture, as supplemented and amended by this Supplemental Indenture, is in all respects hereby adopted, ratified and confirmed.

SECTION 3.2 Counterparts. This Supplemental Indenture may be executed in any number of counterparts, each of which when so executed shall be deemed an original, and all such counterparts shall together constitute but one and the same instrument.

SECTION 3.3 Governing Law. THIS SUPPLEMENTAL INDENTURE AND EACH SECURITY SHALL BE GOVERNED BY AND CONSTRUED IN ACCORDANCE WITH THE LAWS OF THE STATE OF NEW YORK.

SECTION 3.4 Conflict with Trust Indenture Act. If any provision hereof limits, qualifies or conflicts with a provision of the Trust Indenture Act that is required under such Act to be a part of and govern this Supplemental Indenture, the latter provision shall control. If any provision of this Supplemental Indenture modifies or excludes any provision of the Trust Indenture Act that may be so modified or excluded, the latter provision shall be deemed to apply to this Supplemental Indenture as so modified or to be excluded, as the case may be.

[Signature Page Follows]

IN WITNESS WHEREOF, the parties hereto have caused this Supplemental Indenture No. 3 to be duly executed as of the day and year first above written.

[SIGNATURE PAGE TO SUPPLEMENTAL INDENTURE NO. 3]

[SIGNATURE PAGE TO SUPPLEMENTAL INDENTURE NO. 3]

Exhibit A

[FORM FACE OF NOTE]

THIS SECURITY IS A BOOK-ENTRY SECURITY WITHIN THE MEANING OF THE INDENTURE HEREINAFTER REFERRED TO AND IS REGISTERED IN THE NAME OF A DEPOSITORY OR A NOMINEE OF A DEPOSITORY. THIS SECURITY IS EXCHANGEABLE FOR SECURITIES REGISTERED IN THE NAME OF A PERSON OTHER THAN THE DEPOSITORY OR ITS NOMINEE ONLY IN THE LIMITED CIRCUMSTANCES DESCRIBED IN THE INDENTURE AND MAY NOT BE TRANSFERRED EXCEPT AS A WHOLE BY THE DEPOSITORY TO A NOMINEE OF THE DEPOSITORY OR BY A NOMINEE OF THE DEPOSITORY TO THE DEPOSITORY OR ANOTHER NOMINEE OF THE DEPOSITORY.

ONE GAS, INC.

2.00% Senior Notes due 2030

ONE Gas, Inc., a corporation duly organized and existing under the laws of Oklahoma (herein called the “Company,” which term includes any successor Person under the Indenture hereinafter referred to), for value received, hereby promises to pay to , or registered assigns, the principal sum of                 , and to pay interest thereon from May 4, 2020 or from the most recent Interest Payment Date (as defined below) to which interest has been paid or duly provided for, semi-annually on May 15 and November 15 (each such date, an “Interest Payment Date”) and in each year, commencing November 15, 2020, at the rate of 2.00% per annum, until the principal hereof is paid or made available for payment, and (to the extent that the payment of such interest shall be legally enforceable) at the same rate on any overdue principal and premium and on any overdue installment of interest. The interest so payable, and punctually paid or duly provided for, on any Interest Payment Date will, as provided in such Indenture, be paid to the Person in whose name this Security (or one or more Predecessor Securities) is registered at the close of business on the Regular Record Date (as defined below) for such interest, which shall be (a) the May 1 or November 1 (whether or not a Business Day), as the case may be, immediately preceding such Interest Payment Date or (b) so long as this note is a global note in book-entry form on the Business Day immediately preceding such Interest Payment Date. Any such interest not so punctually paid or duly provided for will forthwith cease to be payable to the Holder on such Regular Record Date (each a “Regular Record Date”) and may either be paid to the Person in whose name this Security (or one or more Predecessor Securities) is registered at the close of business on a Special Record Date for the payment of such Defaulted Interest to be fixed by the Trustee, notice whereof shall be given to Holders of Securities of this series not less than 10 days prior to such Special Record Date, or be paid at any time in any other lawful manner not inconsistent with the requirements of any securities exchange on which the Securities of this series may be listed, and upon such notice as may be required by such exchange, all as more fully provided in said Indenture.

Reference is hereby made to the further provisions of this Security set forth on the reverse hereof, which further provisions shall for all purposes have the same effect as if set forth at this place.

Unless the certificate of authentication hereon has been executed by the Trustee referred to on the reverse hereof by manual signature, this Security shall not be entitled to any benefit under the Indenture or be valid or obligatory for any purpose.

IN WITNESS WHEREOF, the Company has caused this instrument to be duly executed.

Dated:

TRUSTEE’S CERTIFICATE OF AUTHENTICATION

This is one of the Securities of the series designated therein referred to in the within-mentioned Indenture.

Dated: May 4, 2020

[SIGNATURE PAGE TO GLOBAL NOTE]

[REVERSE OF NOTE]

ONE GAS, INC.

2.00% Senior Notes Due 2030

This Security is one of a duly authorized issue of securities of the Company (herein called the “Securities”), issued and to be issued in one or more series under an Indenture, dated as of January 27, 2014, as it may be supplemented or amended from time to time (herein called the “Indenture”), between the Company and U.S. Bank National Association, as Trustee (herein called the “Trustee”, which term includes any successor trustee under the Indenture), to which Indenture and all indentures supplemental thereto reference is hereby made for a statement of the respective rights, limitations of rights, duties and immunities thereunder of the Company, the Trustee and the Holders of the Securities and of the terms upon which the Securities are, and are to be, authenticated and delivered. This Security is one of the series designated on the face hereof, limited in aggregate principal amount to $300,000,000.

Prior to February 15, 2030, the Company may redeem this Security in whole or in part, at a “make-whole” redemption price equal to the greater of (1) 100% of the principal amount being redeemed or (2) the sum of the present values of the remaining scheduled payments of the principal and interest (other than accrued interest) on this Security being redeemed that would be due if this Security matured on February 15, 2030, discounted to the redemption date on a semi-annual basis (assuming a 360-day year consisting of twelve 30-day months) at the Treasury Rate plus 25 basis points for the notes plus in each of (1) and (2) above, accrued interest to, but excluding, the redemption date.

At any time on or after February 15, 2030, the Company may redeem this Security, at its option, in whole or in part, at a redemption price equal to 100% of the principal amount of the notes then outstanding to be redeemed, plus accrued and unpaid interest thereon to, but excluding, the date of redemption.

The Indenture contains provisions for defeasance at any time of the entire indebtedness of this Security or certain restrictive covenants and Events of Default with respect to this Security, in each case upon compliance with certain conditions set forth therein.

The Indenture permits, with certain exceptions as therein provided, the amendment thereof and the modification of the rights and obligations of the Company and the rights of the Holders of the Securities of each series to be affected under the Indenture at any time by the Company and the Trustee with the consent of the Holders of not less than a majority in principal amount of the Securities at the time Outstanding of each series to be affected. The Indenture also contains provisions permitting the Holders of specified percentages in principal amount of the Securities at the time Outstanding of any series, on behalf of the Holders of all Securities of such series, to waive compliance by the Company with certain provisions of the Indenture and certain past defaults under the Indenture and their consequences. Any such consent or waiver by the Holder of this Security shall be conclusive and binding upon such Holder and upon all future Holders of this Security and of any Security issued upon the registration of transfer hereof or in exchange herefor or in lieu hereof, whether or not notation of such consent or waiver is made upon this Security.

No reference herein to the Indenture and no provision of this Security or of the Indenture shall alter or impair the obligation of the Company, which is absolute and unconditional, to pay the principal of and any premium and interest on this Security at the times, place and rate, and in the coin or currency, herein prescribed.

As provided in the Indenture and subject to certain limitations therein set forth, the transfer of this Security is registerable in the Security Register, upon surrender of this Security for registration of transfer at the office or agency of the Company in any place where the principal of and any premium and interest on this Security are payable, duly endorsed by, or accompanied by a written instrument of transfer in form satisfactory to the Company and the Security Registrar duly executed by, the Holder hereof or his attorney duly authorized in writing, and thereupon one or more new Securities of this series and of like tenor, of authorized denominations and for the same aggregate principal amount, will be issued to the designated transferee or transferees.

The Securities of this series are issuable only in registered form without coupons in denominations of $2,000 and whole multiples of $1,000 in excess thereof. As provided in the Indenture and subject to certain limitations therein set forth, Securities of this series are exchangeable for a like aggregate principal amount of Securities of this series and of like tenor of a different authorized denomination, as requested by the Holder surrendering the same.

No service charge shall be made for any such registration of transfer or exchange, but the Company may require payment of a sum sufficient to cover any tax or other governmental charge payable in connection therewith.

Prior to due presentment of this Security for registration of transfer, the Company, the Trustee and any agent of the Company or the Trustee may treat the Person in whose name this Security is registered as the owner hereof for all purposes, whether or not this Security be overdue, and neither the Company, the Trustee nor any such agent shall be affected by notice to the contrary.

All terms used in this Security which are defined in the Indenture shall have the meanings assigned to them in the Indenture.

This Security shall be governed by and construed in accordance with the laws of the State of New York.