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 17, 2015

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

(Former name or former address, if changed since last report): Not applicable

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 August 17, 2015, Plains All American Pipeline, L.P. (the “Partnership”) and PAA Finance Corp. (“PAA Finance,” and together with the Partnership, the “Issuers”) entered into an underwriting agreement (the “Underwriting Agreement”) with Citigroup Global Markets Inc., Mizuho Securities USA Inc., Mitsubishi UFJ Securities (USA), Inc. and UBS Securities LLC, as representatives of the several underwriters named therein (collectively, the “Underwriters”), relating to the issuance and sale to the Underwriters of $1.0 billion aggregate principal amount of 4.65% Senior Notes due 2025 (the “Notes”), subject to the terms and conditions therein.

The Notes are being offered and sold under the Issuers’ shelf registration statement on Form S-3 (Registration No. 333-184137) filed with the Securities and Exchange Commission on September 27, 2012 (the “Registration Statement”), and are described in a Prospectus Supplement dated August 17, 2015 to the Prospectus dated September 27, 2012, which is included in the Registration Statement.

The Notes will be issued pursuant to a supplemental indenture to be dated August 24, 2015 by and among the Issuers and U.S. Bank National Association (successor to Wachovia Bank, National Association), as trustee (the “Trustee”). The supplemental indenture will be entered into in accordance with the provisions of the Indenture dated September 25, 2002 by and among the Issuers and the Trustee.

The closing of the offering of the Notes is expected to occur on August 24, 2015, subject to customary closing conditions.

The Underwriting Agreement is filed as Exhibit 1.1 to this Current Report on Form 8-K and is incorporated herein by reference.

(d) Exhibits.

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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: August 19, 2015

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EXHIBIT INDEX

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