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): June 27, 2012

AMERICAN MIDSTREAM PARTNERS, LP

(Exact name of registrant as specified in its charter)

Registrant’s telephone number, including area code: (720) 457-6060

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 (see General Instruction A.2. below):

Item 1.01 Entry into a Material Definitive Agreement.

American Midstream Partners, LP (the “Partnership”) entered into a Second Amendment to Credit Agreement, dated as of June 27, 2012. The Second Amendment provides for an increase in the borrowing capacity from $100 million to $200 million. The material terms and conditions of the senior secured revolving credit facility, including pricing, maturity and covenants, remain unchanged. The credit facility matures in August 2016.

A copy of the Second Amendment is filed as Exhibit 10.1 to this Current Report on Form 8-K and is 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 Partnership entered into a Second Amendment to Credit Agreement, dated as of June 27, 2012. The Second Amendment provides for an increase in the borrowing capacity from $100 million to $200 million. The material terms and conditions of the senior secured revolving credit facility, including pricing, maturity and covenants, remain unchanged. The credit facility matures in August 2016. As of the execution of the Second Amendment, the total debt outstanding under the Partnership’s credit facility was $70.6 million.

A copy of the Second Amendment is filed as Exhibit 10.1 to this Current Report on Form 8-K and is incorporated herein by reference.

Item 7.01 Regulation FD Disclosure.

On June 27, 2012, the Partnership announced the amendment of its senior secured revolving credit facility to increase the borrowing capacity from $100 million to $200 million. A copy of the press release is attached as Exhibit 99.1 to this Current Report on Form 8-K and is incorporated by reference.

In accordance with General Instruction B.2 of Form 8-K, the information set forth in this Item 7.01 and the attached Exhibit 99.1 is deemed to be “furnished” and shall not be deemed to be “filed” for purposes of Section 18 of the Securities Exchange Act of 1934, as amended (the “Exchange Act”).

Item 9.01 Financial Statements and Exhibits.

(d) Exhibits. See “Exhibits Index” attached to this Current Report on Form 8-K, which is incorporated by reference herein.

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.

Exhibit Index