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) May 7, 2015

Commission File Number: 1-14222

SUBURBAN PROPANE PARTNERS, L.P.

(Exact name of registrant as specified in its charter)

240 Route 10 West

Whippany, New Jersey 07981

(973) 887-5300

(Address, including zip code, and telephone number, including

area code, of registrant’s principal executive offices)

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 2.02. RESULTS OF OPERATIONS AND FINANCIAL CONDITION

The following information, including the exhibit attached hereto, shall not be deemed “filed” for purposes of Section 18 of the Securities Exchange Act of 1934, as amended (the “Exchange Act”), or incorporated by reference in any filing under the Securities Act of 1933, as amended, or the Exchange Act, except as shall be expressly set forth by specific reference in such a filing.

On May 7, 2015, Suburban Propane Partners, L.P. issued a press release (the “Press Release”) describing its Fiscal 2015 Second Quarter Financial Results. A copy of the Press Release has been furnished as Exhibit 99.1 to this Current Report.

Within the Press Release, we reference net income before deducting interest expense, income taxes, depreciation and amortization (“EBITDA”) which is considered a non-GAAP financial measure. Additionally, we discuss EBITDA excluding the unrealized net gain or loss from mark-to-market activity for derivative instruments and certain other items (“Adjusted EBITDA”). Our calculations of EBITDA and Adjusted EBITDA are presented in the Press Release furnished as Exhibit 99.1 to this Current Report.

We provide these non-GAAP financial measures because we believe that they provide the investment community with supplemental measures of operating performance. In addition, we believe that these non-GAAP financial measures provide useful information to investors and industry analysts to evaluate our operating results.

We also reference gross margins, computed as revenues less cost of products sold as those amounts are reported on the consolidated financial statements. Since cost of products sold does not include depreciation and amortization expense, the gross margin we reference is considered a non-GAAP financial measure. Given the nature of our business, the level of profitability in the retail propane, fuel oil, and natural gas and electricity businesses is largely dependent on the difference between retail sales price and product cost. Therefore, we discuss gross margins in order to provide investors and industry analysts with useful information to facilitate their understanding of the impact of the commodity prices on profitability.

ITEM 9.01. FINANCIAL STATEMENTS AND 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.

EXHIBITS