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): September 15, 2016

Northern Tier Energy LP

(Exact name of registrant as specified in its charter)

1250 W. Washington Street, Suite 300

Tempe, Arizona 85281

(Address of principal executive office) (Zip Code)

(602) 302-5450

(Registrant’s telephone number, including area code)

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:

Introductory Note

On September 15, 2016, St. Paul Park Refining Co. LLC (“SPPR”), an indirect wholly owned subsidiary of Western Refining, Inc. (“Western”) and wholly owned subsidiary of Northern Tier Energy LLC, which is a wholly owned subsidiary of Northern Tier Energy LP (the “Partnership”), completed the previously announced sale of certain storage, terminalling and other logistics assets to Western Refining Logistics, LP (“WNRL”), pursuant to a Contribution, Conveyance and Assumption Agreement, dated September 7, 2016 (the “Contribution Agreement”), by and among Western, SPPR, WNRL and Western Refining Logistics GP, LLC, the general partner of WNRL (the “WRGP”). Pursuant to the terms of the Contribution Agreement, SPPR sold to WNRL approximately four million barrels of refined product and crude oil storage tanks, a light products terminal, a heavy products loading rack, certain rail and barge facilities, certain other related logistics assets, and two crude oil pipeline segments and one pipeline segment not currently in service, each of which is approximately 2.5 miles and extends from SPPR’s refinery in St. Paul Park, Minnesota to SPPR’s tank farm in Cottage Grove, Minnesota, in exchange for total consideration of $210 million, comprised of $195 million in cash and $15 million of common units representing limited partner interests in WNRL issued to SPPR (collectively with the transactions contemplated by the Contribution Agreement, the “Transaction”). WNRL issued 628,224 common units to SPPR, representing $15 million of common units, based upon the volume-weighted average price per unit for the 20-day trading period ended September 6, 2016.

In connection with the closing of the Transaction, on September 15, 2016, SPPR entered into a terminalling, transportation and storage services agreement (the “Terminalling Agreement”) with Western Refining Terminals, LLC (“WRT”), an indirect, wholly owned subsidiary of WNRL. Pursuant to the Terminalling Agreement, WRT has agreed to provide product storage services, product throughput services and product additive and blending services at the terminal facilities located at or near SPPR’s refinery in St. Paul Park, Minnesota. In exchange for such services, SPPR has agreed to certain minimum volume commitments and to pay certain fees. In connection with the execution of the Terminalling Agreement, the Partnership has agreed to guarantee SPPR’s payment obligations under the Terminalling Agreement. The Terminalling Agreement will have an initial term of ten years, which may be extended for up to two renewal terms of five years each upon the mutual agreement of the parties.

The foregoing description of the Terminalling Agreement is not complete and is qualified in its entirety by reference to the text of the Terminalling Agreement, which is attached to this Current Report on Form 8-K as Exhibit 10.1 and is incorporated in this Item 1.01 by reference.

Relationships

Each of the Partnership, SPPR, WNRL, WRGP and WRT is a direct or indirect subsidiary or affiliate of Western. As a result, certain individuals, including officers and directors of Western and WRGP, serve as officers and/or directors of more than one of such other entities. Western owns through its wholly owned subsidiaries all of the limited partner interests and general partner interests in the Partnership. Western also owns through its wholly owned subsidiaries 9,207,847 common units (including 628,224 common units issued to SPPR in connection with the closing of the Transaction) representing limited partner interests of WNRL and all of the subordinated units representing limited partner interests in WNRL. In addition, Western owns, through its wholly owned subsidiary, Western Refining Southwest, Inc., 80,000 units of a class of limited partner interests in WNRL referred to as the “TexNew Mex Units.” WRGP also owns a non-economic general partner interest in WNRL.

To the extent required, the information set forth under “Introductory Note” and Item 1.01 of this Current Report on Form 8-K is incorporated herein by reference. A copy of the Contribution Agreement was filed as Exhibit 2.1 to the Current Report on Form 8-K filed by the Partnership with the Securities and Exchange Commission on September 7, 2016, and is incorporated herein by reference.

SIGNATURES

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

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