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): March 6, 2012

Plains All American Pipeline, L.P.

(Exact name of registrant as specified in its charter)

Registrant’s telephone number, including area code: (713) 646-4100

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):

On March 6, 2012, Plains All American Pipeline, L.P. (the “Partnership”) entered into an Underwriting Agreement (the “Underwriting Agreement”) with Barclays Capital Inc., Merrill Lynch, Pierce, Fenner & Smith Incorporated, Citigroup Global Markets Inc., J.P. Morgan Securities LLC, UBS Securities LLC and Wells Fargo Securities, LLC, as representatives of the several underwriters named therein (the “Underwriters”), that provides for the issuance and sale by the Partnership, and purchase by the Underwriters, of 5,750,000 common units representing limited partner interests in the Partnership (the “Common Units”), which amount includes 750,000 common units purchased pursuant to the full exercise of the Underwriters’ over-allotment option. The material terms of the offering of the Common Units are described in the prospectus supplement, dated March 6, 2012, as filed by the Partnership with the Securities and Exchange Commission (the “Commission”). The offer and sale of the Common Units was registered with the Commission pursuant to an automatic shelf registration statement on Form S-3 (Registration No. 333-162475) filed by the Partnership on October 14, 2009. Closing with respect to the Common Units is expected to occur on March 9, 2012, subject to the satisfaction of customary closing conditions.

The Underwriting Agreement contains customary representations, warranties and agreements of the Partnership and certain affiliates, and customary conditions to closing, indemnification rights, obligations of the parties and termination provisions. Furthermore, the Partnership, its general partner, certain officers and directors and its general partner and certain of their affiliates have agreed with the Underwriters not to offer or sell any common units (or securities convertible into or exchangeable for common units), subject to customary exceptions, for a period of 45 days after the date of the Underwriting Agreement without the prior written consent of Barclays Capital Inc.

Each of the Underwriters or their respective affiliates have performed investment and commercial banking and advisory services for the Partnership and its affiliates from time to time for which they have received customary fees and expenses. The Underwriters and their affiliates may, from time to time, engage in transactions with and perform services for the Partnership in the ordinary course of their business. Affiliates of certain of the Underwriters are lenders under the Partnership’s credit facilities and accordingly may receive a portion of the proceeds from the offering pursuant to any repayment of borrowings under such facilities.

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. Legal opinions relating to the offering of the Common Units are attached hereto as Exhibits 5.1 and 8.1.

On March 6, 2012, the Partnership issued a press release announcing that it had priced the offering described in Item 1.01 of this Current Report on Form 8-K. A copy of the press release is furnished as Exhibit 99.1 hereto.

In accordance with General Instruction B.2 of Form 8-K, the disclosure in this Item 7.01 and Exhibit 99.1 is deemed to be “furnished” and shall not be deemed “filed” for the purpose of Section 18 of the Securities Exchange Act of 1934, as amended, or otherwise subject to the liabilities of that section, nor shall such information and Exhibit 99.1 be deemed incorporated by reference into any filing under the Securities Act of 1933 or the Securities Exchange Act of 1934, each as amended.

(d) Exhibits.

2

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.

Date: March 8, 2012

EXHIBIT INDEX