FIRST SUPPLEMENTAL INDENTURE

Exhibit 4.2

EXECUTION COPY

FIRST SUPPLEMENTAL INDENTURE

between

MARITIMES & NORTHEAST PIPELINE, L.L.C.

and

DEUTSCHE BANK TRUST COMPANY AMERICAS,

as Trustee

May 14, 2009

7.5% Senior Notes due 2014

TABLE OF CONTENTS

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FIRST SUPPLEMENTAL INDENTURE

THIS FIRST SUPPLEMENTAL INDENTURE, dated as of May 14, 2009 (this “First Supplemental Indenture”), between Maritimes & Northeast Pipeline, L.L.C.., a Delaware limited liability company (the “Issuer” or the “Company”), and Deutsche Bank Trust Company Americas, a New York banking corporation, as trustee (the “Trustee”),

W I T N E S S E T H:

WHEREAS, the Issuer has heretofore executed and delivered to the Trustee an Indenture, dated as of even date herewith (the “Original Indenture” and, as amended and supplemented by this First Supplemental Indenture, the “Indenture”), providing for the issuance from time to time of one or more series of the Company’s Notes;

WHEREAS, Section 9.01(g) of the Indenture provides that the Issuer and the Trustee may from time to time enter into one or more indentures supplemental thereto to establish the form or terms of Notes of a new series;

WHEREAS, the Issuer desires to issue, as the initial series of Notes under the Indenture, $585,000,000 aggregate principal amount of 7.5% Senior Notes due 2014 (the “2014 Notes”), the issuance of which has been authorized by a Management Committee Resolution;

WHEREAS, the Issuer, pursuant to the foregoing authority, proposes in and by this First Supplemental Indenture to supplement and amend the Original Indenture, but only insofar as it will apply to the 2014 Notes; and

WHEREAS, all things necessary have been done to make the 2014 Notes, when issued, authenticated and delivered under the Indenture, the valid obligations of the Issuer, and to make this First Supplemental Indenture a valid and legally binding agreement of the Issuer, in accordance with their and its terms;

NOW, THEREFORE:

In consideration of the premises provided for herein, the Issuer and the Trustee mutually covenant and agree for the equal and proportionate benefit of all holders of the 2014 Notes as follows:

ARTICLE 1

THE 2014 NOTES

SECTION 1.1. Designation of Notes; Establishment of Form.

There shall be a series of Notes designated “7.5% Senior Notes due 2014” of the Issuer, and the form thereof shall be substantially as set forth in Exhibit A hereto, which is incorporated into and shall be deemed a part of this First Supplemental Indenture, and may have such letters, numbers or other marks of identification or designation and such legends or endorsements placed thereon as may, consistently with the Indenture, be determined by the officers of the managing member of the Issuer executing such 2014 Notes, as evidenced by their execution of the 2014 Notes.

The 2014 Notes will initially be issued exclusively in the form of one or more Global Notes, and The Depository Trust Company is hereby designated by the Issuer as the Depositary with respect to the 2014 Notes.

SECTION 1.2. Amount, Etc.

The Trustee shall authenticate and deliver 2014 Notes for original issue in an aggregate principal amount of $500,000,000, all upon delivery to the Trustee of a written order by the Issuer for the authentication and delivery of 2014 Notes.

2014 Notes aggregating $500,000,000 shall be issued in the form of a Rule 144A Global Note, and a “zero balance” Regulation S Temporary Global Note shall also be issued for later use.

The authorized aggregate principal amount of 2014 Notes may be increased at any time hereafter and such series may be reopened for issuances of additional 2014 Notes as provided in the last paragraph of Section 2.01 of the Original Indenture, so long as (i) no Event of Default has occurred and is then continuing with respect to the 2014 Notes and (ii) such additional 2014 Notes are fungible for U.S. federal income tax purposes with the 2014 Notes issued on the date hereof so that such additional 2014 Notes will trade as part of a single series with the 2014 Notes issued on the date hereof. The 2014 Notes issued on the date hereof and any additional 2014 Notes that may be issued hereafter shall be treated as a single class for all purposes of the Indenture, including waivers, amendments, redemption and offers to purchase.

Unless the context otherwise requires, all references in the Indenture to the 2014 Notes include the 2014 Notes issued on the date hereof and any additional 2014 Notes that may be issued hereafter.

Any other series of Notes that may be issued under the Indenture after the date hereof shall not vote together with the 2014 Notes as a single series or class on any matters.

SECTION 1.3. Redemption and Repurchase.

There shall be no sinking fund for the retirement of the 2014 Notes or other mandatory redemption or repurchase obligation.

The Issuer, at its option, may redeem the 2014 Notes in accordance with the provisions of the form of the 2014 Notes set forth in Exhibit A hereto and Article Three of the Original Indenture. With respect to the 2014 Notes, the number of basis points referred to in the definition of “Make-Whole Premium” in Section 1.01 of the Original Indenture is 50.

SECTION 1.4. Conversion.

The 2014 Notes shall not be convertible into any other securities.

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SECTION 1.5. Maturity.

The principal of the 2014 Notes shall mature in installments as provided in the form of the 2014 Notes set forth in Exhibit A, and the Final Maturity Date of the 2014 Notes shall be May 31, 2014.

SECTION 1.6. Other Terms of Notes.

Without limiting the foregoing provisions of this Article 1, the terms of the 2014 Notes shall be as provided in the form of the 2014 Notes set forth in Exhibit A hereto and as provided in the Indenture.

ARTICLE 2

MISCELLANEOUS PROVISIONS

SECTION 2.1. Integral Part.

This First Supplemental Indenture constitutes an integral part of the Indenture.

SECTION 2.2. Rules of Construction.

For all purposes of this First Supplemental Indenture:

(a) capitalized terms used herein without definition shall have the meanings specified in the Original Indenture;

(b) the terms “herein,” “hereof,” “hereunder” and other words of similar import refer to this First Supplemental Indenture; and

(c) references to the “Notes” in the definition of “Permitted Refinancing Indebtedness” in the Original Indenture and in the proviso to clause (ii) of Section 4.13 thereof shall be deemed to refer only to the 2014 Notes.

SECTION 2.3. Adoption, Ratification and Confirmation.

The Original Indenture, as supplemented and amended by the First Supplemental Indenture, is in all respects hereby adopted, ratified and confirmed.

SECTION 2.4. Counterparts.

This First 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. The exchange of copies of this First Supplemental Indenture and of signature pages by facsimile or PDF transmission shall constitute effective execution and delivery of this First Supplemental Indenture as to the parties hereto and may be used in lieu of the original First Supplemental Indenture for all purposes. Signatures of the parties hereto transmitted by facsimile or PDF shall be deemed to be their original signatures for all purposes.

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SECTION 2.5. Benefits of Indenture.

Nothing in this First Supplemental Indenture or in the 2014 Notes, express or implied, shall give to any Person (other than the parties hereto and the holders of the 2014 Notes) any benefit or any legal or equitable right, remedy or claim under the Indenture.

SECTION 2.6. Governing Law.

THIS FIRST SUPPLEMENTAL INDENTURE AND THE 2014 NOTES SHALL BE GOVERNED BY AND CONSTRUED IN ACCORDANCE WITH THE LAWS OF THE STATE OF NEW YORK

SECTION 2.7. Supplemental Indenture Controls.

In the event there is any conflict or inconsistency between the Original Indenture and this First Supplemental Indenture, the provisions of this First Supplemental Indenture shall control.

SECTION 2.8. Trustee.

The Trustee makes no representations as to the validity or sufficiency of this First Supplemental Indenture. The recitals and statements herein are deemed to be those of the Issuer and not the Trustee.

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IN WITNESS WHEREOF , the parties hereto have caused this First Supplemental Indenture to be duly executed as of the day and year first written above.

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EXHIBIT A

FORM OF NOTE

[FORM OF FACE OF 2014 NOTE]

[INCLUDE IF NOTE IS A REGULATION S TEMPORARY NOTE]

THE RIGHTS ATTACHING TO THIS REGULATION S TEMPORARY GLOBAL NOTE, AND THE CONDITIONS AND PROCEDURES GOVERNING ITS EXCHANGE FOR CERTIFICATED NOTES, ARE AS SPECIFIED IN THE INDENTURE (AS DEFINED HEREIN). NEITHER THE HOLDER NOR THE BENEFICIAL OWNERS OF THIS REGULATION S TEMPORARY GLOBAL NOTE SHALL BE ENTITLED TO RECEIVE PAYMENT OF INTEREST HEREON.

[INCLUDE IF NOTE IS A GLOBAL NOTE]

UNLESS THIS NOTE IS PRESENTED BY AN AUTHORIZED REPRESENTATIVE OF THE DEPOSITORY TRUST COMPANY (55 WATER STREET, NEW YORK, NEW YORK) (“DTC”) TO THE COMPANY OR ITS AGENT FOR REGISTRATION OF TRANSFER, EXCHANGE OR PAYMENT, AND ANY NOTE IS REGISTERED IN THE NAME OF CEDE & CO., OR IN SUCH OTHER NAME AS IS REQUESTED BY AN AUTHORIZED REPRESENTATIVE OF DTC (AND ANY PAYMENT IS MADE TO CEDE & CO. OR TO SUCH OTHER ENTITY AS IS REQUESTED BY AN AUTHORIZED REPRESENTATIVE OF DTC), ANY TRANSFER, PLEDGE OR OTHER USE HEREOF FOR VALUE OR OTHERWISE BY OR TO ANY PERSON IS WRONGFUL INASMUCH AS THE REGISTERED OWNER HEREOF, CEDE & CO., HAS AN INTEREST HEREIN.

TRANSFERS OF THIS NOTE SHALL BE LIMITED TO TRANSFERS IN WHOLE, BUT NOT IN PART, TO DTC, TO NOMINEES OF DTC OR TO A SUCCESSOR THEREOF OR SUCH SUCCESSOR’S NOMINEE AND TRANSFERS OF PORTIONS OF THIS NOTE SHALL BE LIMITED TO TRANSFERS MADE IN ACCORDANCE WITH THE RESTRICTIONS SET FORTH IN SECTION 2.06 OF THE INDENTURE REFERRED TO ON THE REVERSE HEREOF.

[INCLUDE IF NOTE IS A RULE 144A GLOBAL NOTE OR ANY CERTIFICATED NOTE ISSUED IN ACCORDANCE WITH SECTION 2.05 OF THE INDENTURE IN EXCHANGE FOR SUCH A GLOBAL NOTE]

THIS NOTE HAS NOT BEEN REGISTERED UNDER THE U.S. SECURITIES ACT OF 1933, AS AMENDED (THE “SECURITIES ACT”), AND, ACCORDINGLY, MAY NOT BE OFFERED, SOLD, PLEDGED OR OTHERWISE TRANSFERRED WITHIN THE UNITED STATES OR TO, OR

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FOR THE ACCOUNT OR BENEFIT OF, U.S. PERSONS, EXCEPT AS SET FORTH IN THE FOLLOWING SENTENCE. BY ITS ACQUISITION HEREOF OR OF A BENEFICIAL INTEREST HEREIN, THE HOLDER:

(1) REPRESENTS THAT IT IS A “QUALIFIED INSTITUTIONAL BUYER” (AS DEFINED IN RULE 144A UNDER THE SECURITIES ACT) (A “QIB”);

(2) AGREES THAT IT WILL NOT, PRIOR TO THE EXPIRATION OF THE HOLDING PERIOD APPLICABLE TO SALES OF THIS NOTE UNDER RULE 144 UNDER THE SECURITIES ACT (OR ANY SUCCESSOR PROVISION), RESELL OR OTHERWISE TRANSFER THIS NOTE EXCEPT (A) TO THE ISSUER OR ANY OF ITS SUBSIDIARIES, (B) TO A PERSON WHOM THE SELLER REASONABLY BELIEVES IS A QIB PURCHASING FOR ITS OWN ACCOUNT OR FOR THE ACCOUNT OF A QIB IN A TRANSACTION MEETING THE REQUIREMENTS OF RULE 144A, (C) IN AN OFFSHORE TRANSACTION MEETING THE REQUIREMENTS OF REGULATION S UNDER THE SECURITIES ACT, (D) IN A TRANSACTION MEETING THE REQUIREMENTS OF RULE 144 UNDER THE SECURITIES ACT, (E) IN ACCORDANCE WITH ANOTHER EXEMPTION FROM THE REGISTRATION REQUIREMENTS OF THE SECURITIES ACT (AND BASED UPON AN OPINION OF COUNSEL ACCEPTABLE TO THE ISSUER), OR (F) PURSUANT TO AN EFFECTIVE REGISTRATION STATEMENT UNDER THE SECURITIES ACT AND, IN EACH CASE, IN ACCORDANCE WITH THE APPLICABLE SECURITIES LAWS OF ANY STATE OF THE UNITED STATES OR ANY OTHER APPLICABLE JURISDICTION; AND

(3) AGREES THAT IT WILL DELIVER TO EACH PERSON TO WHOM THIS NOTE OR AN INTEREST HEREIN IS TRANSFERRED A NOTICE SUBSTANTIALLY TO THE EFFECT OF THIS LEGEND.

AS USED HEREIN, THE TERMS “OFFSHORE TRANSACTION” AND “UNITED STATES” HAVE THE MEANINGS GIVEN TO THEM BY RULE 902 OF REGULATION S UNDER THE SECURITIES ACT. THE INDENTURE GOVERNING THIS NOTE CONTAINS A PROVISION REQUIRING THE TRUSTEE TO REFUSE TO REGISTER ANY TRANSFER OF THIS NOTE IN VIOLATION OF THE FOREGOING RESTRICTIONS.

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MARITIMES & NORTHEAST PIPELINE, L.L.C.

7.5% SENIOR NOTE DUE 2014

MARITIMES & NORTHEAST PIPELINE, L.L.C., a limited liability company duly organized and existing under the laws of the State of Delaware (herein referred to as the “ Issuer ” or the “ Company ,” which term includes any successor Person under the Indenture), for value received, hereby promises to pay to                      or registered assigns, the principal sum equal to              Dollars ($            ) [Insert if Note is in a global form—or such other principal sum as shall be set forth in the Schedule of Exchanges of Interests in the Global Note attached hereto], such payment to be made in installments in the amounts and on the Principal Payment Dates indicated in the Installment Payment Schedule attached hereto and to pay interest on the unpaid principal balance hereof from and including May 14, 2009, or from and including the most recent interest payment date (each such date, an “ Interest Payment Date ”) to which interest has been paid or duly provided for, payable semiannually in arrears on May 31 and November 30 of each year, commencing on November 30, 2009 at the rate of 7.5% per annum until all of the principal hereof shall have become due and payable, and on any overdue principal and any Make-Whole Premium, and (to the extent that payment of such interest is enforceable under applicable law) on any overdue installment of interest at the same rate per annum. The amount of interest payable on any Intere