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 (Date of earliest event reported): August 9, 2010

NuStar Energy L.P.

(Exact name of registrant as specified in its charter)

2330 North Loop 1604 West

San Antonio, Texas 78248

(Address of principal executive offices)

(210) 918-2000

(Registrant’s telephone number, including area code)

Not applicable

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

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions:

On August 9, 2010, NuStar Logistics, L.P. (“NuStar Logistics”), NuStar Energy L.P. (“NuStar Energy”), NuStar Pipeline Operating Partnership L.P. (“NuPOP”), Riverwalk Logistics, L.P., NuStar GP, Inc., NuStar GP, LLC and NuStar Pipeline Company, LLC (collectively, the “NuStar Parties”) entered into an underwriting agreement (the “Underwriting Agreement”) with Banc of America Securities LLC, BNP Paribas Securities Corp. and J.P. Morgan Securities Inc., as representatives of the several underwriters named therein (the “Underwriters”), relating to the public offering by NuStar Logistics of $450 million aggregate principal amount of 4.80% Senior Notes due 2020 (the “Notes”). The Notes are being guaranteed (such guarantees together with the Notes, the “Securities”) on a full and unconditional basis by NuStar Energy and NuPOP. The Notes have been registered under the Securities Act of 1933, as amended (the “Securities Act”), pursuant to a Registration Statement on Form S-3 (Registration No. 333-166797), as supplemented by the Prospectus Supplement dated August 9, 2010 relating to the Securities, filed with the Securities and Exchange Commission pursuant to Rule 424(b) of the Securities Act (together with the accompanying prospectus dated March 13, 2010, the “Prospectus Supplement”). Closing of the issuance and sale of the Notes is scheduled for August 12, 2010. Certain legal opinions related to the Notes are filed herewith as Exhibit 5.1 and Exhibit 8.1.

The Underwriting Agreement provides that the obligations of the Underwriters to purchase the Notes are subject to the approval of legal matters by counsel and other customary conditions. The Underwriters are obligated to purchase all the Notes if they purchase any of the Notes. The Underwriting Agreement contains customary representations, warranties and agreements by the NuStar Parties and customary conditions to closing. Additionally, the NuStar Parties have agreed to indemnify the Underwriters against certain liabilities, including liabilities under the Securities Act, or to contribute to payments the Underwriters may be required to make because of these liabilities. The foregoing description of the Underwriting Agreement is qualified in its entirety by reference to such Underwriting Agreement, a copy of which is filed herewith as Exhibit 1.1 and is incorporated herein by reference. The Underwriting Agreement contains certain representations, warranties and other provisions that were made or agreed to, among other things, to provide the parties thereto with specified rights and obligations and to allocate risk among them.

The Prospectus Supplement provides that NuStar Logistics will use net proceeds from the offering to repay a portion of the outstanding balance under its revolving credit facility. Certain of the underwriters and their affiliates have performed, and may in the future perform, investment banking, commercial banking and advisory services for NuStar Logistics and its affiliates and has received, and may in the future receive, fees for these services.

SIGNATURES

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

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