AMENDMENT NO. 1 TO THIRD AMENDED AND RESTATED AGREEMENT OF LIMITED PARTNERSHIP

EXHIBIT 3.1

AMENDMENT NO. 1 TO THIRD AMENDED AND RESTATED

AGREEMENT OF LIMITED PARTNERSHIP OF

ONEOK PARTNERS, L.P.

This Amendment No. 1, dated July 20, 2007 (this “ Amendment ”), to the Third Amended and Restated Agreement of Limited Partnership (the “ Partnership Agreement ”), of ONEOK Partners, L.P., a Delaware limited partnership, dated as of September 15, 2006, is entered into and effectuated by ONEOK Partners GP, L.L.C., a Delaware limited liability company and f/k/a Northern Plains Natural Gas Company, LLC in its capacity as the General Partner, pursuant to authority granted to it in Article XV of the Partnership Agreement. Capitalized terms used but not defined herein are used as defined in the Partnership Agreement.

RECITALS:

WHEREAS, Section 15.1(d)(i) of the Partnership Agreement provides that the General Partner, without the approval of any Partner, may amend any provision of the Partnership Agreement to reflect a change that the General Partner determines does not adversely affect the Limited Partners (including any particular class of Partnership Interests as compared to other classes of Partnership Interests) in any material respect;

WHEREAS, on December 1, 2006, the Partnership entered into the stipulation of settlement (the “ Settlement ”) in connection with the now-dismissed lawsuit, F. Richard Manson v. Northern Plains Natural Gas Company, LLC, et al., C.A. No. 1973-N (Court of Chancery in the State of Delaware, County of New Castle) in which, among other matters, it agreed to make changes to the terms of the Partnership Agreement to (a) amend the definition of “Audit Committee” to provide that at least one member of the Audit Committee will be an audit committee financial expert, and (b) amend the terms of the Class B Units to provide that (i) if the Conversion Approval or Amendment Approval was not obtained, the holder of the Class B Units would be entitled to increased distributions equal to 110% of the distributions due to Common Unitholders instead of 115% as set forth in the original terms of the Class B Units, and (ii) in certain circumstances, the holder of the Class B Units would be entitled to increased distributions equal to 123.5% of the distributions due to Common Unitholders instead of 125% as set forth in the original terms of the Class B Units;

WHEREAS, at a special meeting of Common Unitholders of the Partnership held on March 29, 2007, the Conversion Approval was obtained, and the meeting was adjourned to May 10, 2007 without obtaining the Amendment Approval;

WHEREAS, at the adjourned special meeting of Common Unitholders of the Partnership held on May 10, 2007, the Amendment Approval was not obtained;

WHEREAS, the Audit Committee has determined, pursuant to Section 6.9 of the Partnership Agreement, that amending the Partnership Agreement to reflect the terms of the Settlement and the outcome of the special meeting and the adjourned special meeting referenced

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above is fair and reasonable to the Partnership, and has recommended to the General Partner that such updating amendments to the Partnership Agreement be approved; and

WHEREAS, the General Partner, has determined that it is in the best interest of the Partnership and the Limited Partners, and does not adversely affect the Limited Partners in any material respect, to amend the Partnership Agreement to reflect the outcome of the special meeting and the adjourned special meeting, to reflect the terms of the Settlement and to make such other changes pursuant to Section 15.1(d)(i) as the General Partner deems to be appropriate.

NOW, THEREFORE, it is hereby agreed as follows:

A. Amendment. The Partnership Agreement is hereby amended as follows:

“ Audit Committee ” means a committee of the Board of Directors of the General Partner consisting of three or more members of the Board of Directors appointed by the Board of Directors who meet the independence and other standards required of directors who serve on an audit committee of a board of directors established by (a) the Securities Exchange Act and rules and regulations of the Commission thereunder, (b) the National Securities Exchange on which the Common Units are listed or admitted to trading and (c) the Board of Directors; provided that at least one member of the Audit Committee will be an audit committee financial expert (as defined in Item 407(d)(5) of Regulation S-K, the Standard Instructions for Filing Forms under the Securities Act of 1933, Securities and Exchange Act of 1934, and Energy and Policy Conversion Act of 1975) and provided further that the aforesaid definition cannot be amended other than with the prior approval of a majority of the Outstanding Common Units (excluding Units held by the General Partner and its Affiliates).

“ Class B Subordination Period ”;

“ Class B Unit Arrearage ”;

“ Common Unit Arrearage ”;

“ Conversion Approval Termination Date ”;

“ Cumulative Class B Unit Arrearage ”;

“ Cumulative Common Unit Arrearage ”; and

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“ Section 4.9(b) Distribution Increase Date ”.

“ Class B Distribution Increase Date ” means April 7, 2007; and

“ Conversion Approval Date ” means March 29, 2007.

“ Conversion Approval ” means the approval of a change in the terms of the Class B Units to provide that each Class B Unit shall be convertible from time to time, at the option of the holders thereof, into one Common Unit (subject to appropriate adjustment in the event of any split-up, combination or similar event affecting the Common Units that occurs prior to the conversion of the Class B Units).

Section 4.8 Establishment of Class B Units.

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THE UNITS REPRESENTED BY THIS CERTIFICATE HAVE NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933, AS AMENDED, OR ANY STATE SECURITIES LAW (“ACTS”). THE UNITS HAVE BEEN ACQUIRED