UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 8-K

CURRENT REPORT

PURSUANT TO SECTION 13 OR 15(d) OF THE

SECURITIES EXCHANGE ACT OF 1934

(Date of report) February 5, 2010

(Date of earliest event reported) February 2, 2010

ONEOK PARTNERS, L.P.

(Exact name of registrant as specified in its charter)

100 West Fifth Street; Tulsa, OK

(Address of principal executive offices)

74103

(Zip code)

(918) 588-7000

(Registrant’s telephone number, including area code)

Not Applicable

(Former name or former address, if changed since last report)

Underwriting Agreement

On February 2, 2010, ONEOK Partners, L.P., a Delaware limited partnership (the “Partnership”), entered into an underwriting agreement (the “Underwriting Agreement”) with UBS Securities LLC, Citigroup Global Markets Inc., Merrill Lynch, Pierce, Fenner & Smith Incorporated, Morgan Stanley & Co. Incorporated and Wells Fargo Securities, LLC, as representatives of the several underwriters named therein with respect to the issuance and sale by the Partnership of 5,250,000 common units representing limited partner interests in the Partnership (“Common Units”) in a public offering (together with an over-allotment option granted to the underwriters to purchase up to an additional 787,500 Common Units).

The Underwriting Agreement contains customary representations, warranties and agreements by the Partnership, customary conditions to closing, indemnification obligations of the Partnership and the underwriters, including for liabilities under the Securities Act of 1933, as amended (the “Act”), and termination provisions. The foregoing description of the Underwriting Agreement is qualified in its entirety by reference to such Underwriting Agreement, a copy of which is filed with this Current Report on Form 8-K as Exhibit 1.1 and is incorporated herein by reference.

Prospectus Supplement

On February 2, 2010, pursuant to Rule 424(b)(5) under the Act, the Partnership filed with the Securities and Exchange Commission a prospectus supplement to its shelf registration statement on Form S-3 dated September 15, 2009 (Registration No. 333-161923) relating to the public offering of the Common Units. Exhibits 1.1, 5.1 and 8.1 to this Current Report on Form 8-K relating to the offering of the Common Units are hereby incorporated by reference into such registration statement.

Affiliations

The underwriters and their affiliates have provided in the past and may provide from time to time in the future certain commercial banking, financial advisory, investment banking and other services for the Partnership for which they will receive customary fees. Some of the net proceeds of this offering may be used to pay down borrowings under the Partnership’s $1.0 billion revolving credit agreement. Affiliates of certain of the underwriters are lenders under such revolving credit agreement and will receive their respective share of any repayment by the Partnership of amounts outstanding thereunder.

The Partnership issued a news release on February 2, 2010, attached hereto as Exhibit 99.1, announcing that it had priced the public offering described in Item 1.01 of this Current Report on Form 8-K at $60.75 per Common Unit. In addition, ONEOK Partners GP, L.L.C., the Partnership’s sole general partner and a wholly-owned subsidiary of ONEOK, Inc., will contribute approximately $6.5 million to maintain its two percent

general partner interest in the Partnership. Following completion of the public offering, the Partnership will have approximately 65.2 million Common Units outstanding. This information is not deemed to be “filed” for purposes of Section 18 of the Securities Exchange Act of 1934, as amended, and is not incorporated by reference into any registration statement under the Act.

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SIGNATURE

Pursuant to the requirements of the Securities Exchange Act of 1934, as amended, the registrant has duly caused this report to be signed on its behalf by the undersigned, hereunto duly authorized.

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EXHIBIT INDEX