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 28, 2012

ENERGY TRANSFER PARTNERS, L.P.

(Exact name of Registrant as specified in its charter)

3738 Oak Lawn Avenue,

Dallas, TX 75219

(Address of principal executive offices)

(214) 981-0700

(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:

Item 1.01. Entry into a Material Definitive Agreement.

On June 28, 2012, Energy Transfer Partners, L.P. (the “Partnership”) entered into an Underwriting Agreement (the “Underwriting Agreement”) with Merrill Lynch, Pierce, Fenner & Smith Incorporated, Barclays Capital Inc., Morgan Stanley & Co. LLC, UBS Securities LLC, Citigroup Global Markets Inc., Goldman, Sachs & Co., J.P. Morgan Securities LLC, and Wells Fargo Securities, LLC as joint book-running managers and representatives of the several underwriters named therein (collectively, the “Underwriters”), pursuant to which the Partnership agreed to sell 15,525,000 common units (the “Units”) representing limited partner interests in the Partnership (including 2,025,000 Units pursuant to the full exercise of the Underwriters’ option to purchase additional Units) at a price of $44.57 per Unit ($43.23 per Unit, net of underwriting discounts and commissions). The Units have been registered under the Securities Act of 1933, as amended (the “Securities Act”), pursuant to a Registration Statement on Form S-3ASR (File No. 333-171697) of the Partnership, as supplemented by the Prospectus Supplement dated June 28, 2012 relating to the Units, filed with the Securities and Exchange Commission (“Commission”) pursuant to Rule 424(b) of the Securities Act on June 28, 2012. Legal opinions relating to the Units are included as Exhibits 5.1 and 8.1 hereto.

The Underwriting Agreement contains customary representations, warranties and agreements by the Partnership, and customary conditions to closing, indemnification obligations of the Partnership and the Underwriters, including for liabilities under the Securities Act, other obligations of the parties and termination provisions. The summary of the Underwriting Agreement in this report does not purport to be complete and is qualified in its entirety by reference to the full text of the Underwriting Agreement, which is filed as Exhibit 1.1 hereto, and is incorporated herein by reference.

In the ordinary course of their respective businesses, the underwriters and their affiliates have engaged, and may in the future engage, in financial advisory, commercial banking and/or investment banking transactions with the Partnership and its affiliates for which they received or will receive customary fees and expenses. In particular, Wells Fargo Securities, LLC acted as the Partnership’s financial advisor in connection with its pending merger with Sunoco, Inc. Additionally, Merrill Lynch, Pierce, Fenner & Smith Incorporated is a joint lead arranger and book runner for the Partnership’s amended and restated revolving credit facility. Affiliates of Merrill Lynch, Pierce, Fenner & Smith Incorporated, Barclays Capital Inc., UBS Securities LLC, Goldman, Sachs & Co., J.P. Morgan Securities LLC, Wells Fargo Securities, LLC and RBC Capital Markets, LLC are lenders and agents under the Partnership’s amended and restated revolving credit facility for which they receive interest and fees as provided in the credit agreement related to the facility.

Item 7.01. Regulation FD Disclosure.

On June 28, 2012, the Partnership issued a press release announcing that it had priced the offering of the Units. A copy of the press release is furnished as Exhibit 99.1 hereto and is incorporated herein by reference.

In accordance with General Instruction B.2 of Form 8-K, the information set forth in 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.

Item 9.01. Financial Statements and Exhibits.

(d) Exhibits.

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.