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): November 22, 2017

NuStar Energy L.P.

(Exact name of registrant as specified in its charter)

19003 IH-10 West

San Antonio, Texas 78257

(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:

Indicate by check mark whether the registrant is an emerging growth company as defined in Rule 405 of the Securities Act of 1933 (§230.405 of this chapter) or Rule 12b-2 of the Securities Exchange Act of 1934 (§240.12b-2 of this chapter).

Emerging growth company  ☐

If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 13(a) of the Exchange Act.  ☐

On November 22, 2017, NuStar Logistics, L.P. (“Logistics”) entered into that certain Third Amendment to Amended and Restated Revolving Credit Agreement dated as of November 22, 2017 among Logistics, NuStar Energy L.P. (the “MLP”), NuStar Pipeline Operating Partnership L.P., JPMorgan Chase Bank, N.A., as Administrative Agent, and the lenders party thereto (the “Third Amendment”). The Third Amendment amends that certain Amended and Restated Revolving Credit Agreement among Logistics, as Borrower, the MLP, JPMorgan Chase Bank, N.A., as Administrative Agent, SunTrust Bank and Mizuho Bank, Ltd., as Co-Syndication Agents, Wells Fargo Bank, National Association and PNC Bank, National Association, as Co-Documentation Agents, and the lenders party thereto, as amended (the “Credit Agreement”) to exclude from the calculation of Consolidated Debt under the Credit Agreement the aggregate principal amount outstanding (up to $402,500,000) of the Logistics’ 7.625% Fixed-to-Floating Rate Subordinated Notes due 2043 for the period from the date of the Third Amendment through December 31, 2018.

Logistics and the MLP also are party to Letter of Credit Agreements with each of Mizuho Bank, Ltd. (dated as of June 5, 2012, as amended), The Bank of Nova Scotia (dated as of June 5, 2013, as amended) and The Bank of Tokyo-Mitsubishi UFJ, Ltd. (dated as of September 3, 2014, as amended) (collectively, the “Letter of Credit Agreements”). Pursuant to the terms of the Letter of Credit Agreements, the corresponding provisions in the Letter of Credit Agreements are deemed automatically amended to conform to the changes made by the Third Amendment.

The above discussion is qualified in its entirety by the text of the Third Amendment, a copy of which is filed as Exhibit 10.01 to this Current Report on Form 8-K and incorporated herein by reference.

Item 2.03 Creation of a Direct Financial Obligation or an Obligation under an Off-Balance Sheet Arrangement of a Registrant.

The description set forth above under Item 1.01 is incorporated by reference into this Item 2.03.

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.