UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, DC 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): April 14, 2015

Atlas Resource Partners, L.P.

(Exact name of registrant as specified in its chapter)

Registrant’s telephone number, including area code: 800-251-0171

(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 3.03. Material Modification to Rights of Security Holders.

The information set forth under Item 5.03 regarding the Certificate of Designation and the LPA Amendment (each as defined below) is incorporated by reference into this Item 3.03.

Item 5.03. Amendments to Articles of Incorporation or Bylaws; Change in Fiscal Year.

On April 14, 2015, in connection with the previously disclosed offering by Atlas Resource Partners, L.P. (the “Partnership”) of its newly-created 10.75% Class E cumulative redeemable perpetual preferred units (the “Class E Units”), the Partnership entered into a Certificate of Designation of the Powers, Preferences and Relative, Participating, Optional, and Other Special Rights and Qualifications, Limitations and Restrictions Thereof (the “Certificate of Designation”) for the Class E Units. Also on April 14, 2015, in connection with its entry into the Certificate of Designation, the Partnership adopted Amendment No. 6 to its Amended and Restated Agreement of Limited Partnership (the “LPA Amendment”) to, among other things, include the Class E Units as authorized preferred units under its partnership agreement.

The Partnership will pay cumulative distributions in cash on the Class E Units on a quarterly basis, at an annual rate of $2.6875 per unit, or 10.75% of the liquidation preference. The Class E Units rank senior to the Partnership’s common units and Class C Preferred Units with respect to the payment of distributions and distributions upon a liquidation event and pari passu with the Partnership’s Class B Preferred Units and Class D Preferred Units. The Class E Units have no stated maturity and are not subject to mandatory redemption or any sinking fund and will remain outstanding indefinitely unless repurchased or redeemed by the Partnership or converted into its common units in connection with a change of control.

At any time on or after April 15, 2020, the Partnership may, at its option, redeem the Class E Units, in whole or in part, at a redemption price of $25.00 per unit plus an amount equal to all accumulated and unpaid distributions thereon to the date of redemption, whether or not declared. In addition, the Partnership may redeem the Class E Units following certain changes of control, as described in the Certificate of Designation. If the Partnership does not exercise this redemption option upon a change of control, then holders of the Class E Units will have the option to convert the Class E Units into a number of Partnership common units per Class E Unit as set forth in the Certificate of Designation. If the Partnership exercises any of its redemption rights relating to the Class E Units, the holders of such Class E Units will not have the conversion right described above with respect to the Class E Units called for redemption.

The foregoing summary of the LPA Amendment and the Certificate of Designation does not purport to be complete and is subject to, and qualified in its entirety by, the full text of the LPA Amendment and the Certificate of Designation, filed as Exhibits 3.1 and 4.1, respectively, to this Current Report, which is incorporated herein by this reference.

Item 9.01. Financial Statements and Exhibits.

Not applicable

Not applicable.

Not applicable.

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 thereunto duly authorized.

EXHIBIT INDEX

Exhibit 5.1

April 14, 2015

Atlas Resource Partners, L.P.

Park Place Corporate Center One

1000 Commerce Drive, 4^th Floor

Pittsburgh, PA 15275

Ladies and Gentlemen:

We have acted as counsel to Atlas Resource Partners, L.P., a Delaware limited partnership (the “Partnership”), in connection with the offering and sale of 255,000 of its 10.75% Class E cumulative redeemable perpetual preferred units representing limited partner interests in the Partnership (the “Units”) pursuant to the Partnership’s registration statement on Form S-3 (Registration No. 333-193727) (the “Registration Statement”), filed under the Securities Act of 1933, as amended (the “Securities Act”). A prospectus supplement dated April 7, 2015, which together with the accompanying prospectus dated February 3, 2014 shall constitute the “Prospectus,” has been filed pursuant to Rule 424(b) promulgated under the Securities Act.

As the basis for the opinions hereinafter expressed, we have examined such statutes, including the Delaware Revised Uniform Limited Partnership Act, as amended (the “Delaware LP Act”), regulations, corporate records and documents, including the Amended and Restated Agreement of Limited Partnership of the Partnership, dated as of March 13, 2012 (as amended to date, the “Partnership Agreement”), certificates of corporate and public officials, and other instruments and documents as we have deemed necessary or advisable for the purposes of this opinion. In making our examination, we have assumed and not verified (i) the genuineness of all signatures on documents examined by us, (ii) the legal capacity of all natural persons, (iii) the authenticity of all documents submitted to us as originals and (iv) the conformity with the original documents of all documents submitted to us as certified, conformed or photostatic copies. We have also assumed that all Units will be issued and sold in the manner described in the Prospectus and in accordance with the terms of the underwriting agreement dated April 7, 2015 relating to the offer and sale of the Units (the “Underwriting Agreement”).

Based upon the foregoing, and subject to the limitations, qualifications, exceptions and assumptions set forth herein, and having due regard for such legal considerations as we deem relevant, we are of the opinion that (i) the issuance of the Units by the Partnership in accordance with the terms of the Underwriting Agreement has been duly authorized by the general partner of the Partnership and (ii) when the Units have been issued and delivered in accordance with the terms of the Underwriting Agreement, the Units will be validly issued, fully paid and non-assessable.

We note, however, that a holder of Units (1) may be obligated to repay any funds distributed to it if such holder knew that such funds were wrongfully distributed to it by the Partnership or (2) if certain rights or actions permitted under the Partnership Agreement were deemed by a court to be “participation in control,” such holder of Units may be held liable for the obligations of the Partnership.

We express no opinion other than as to the federal laws of the United States of America and the Delaware LP Act (including the applicable provisions of the Delaware Constitution and reported judicial decisions interpreting those laws) as in effect and existing on the date hereof.

We consent to the filing by you of this opinion as an exhibit to the Partnership’s Current Report on Form 8-K filed on the date hereof, and we further consent to the use of our name under the caption “Legal Matters” in the Prospectus. In giving these consents, we do not thereby admit that we are within the category of persons whose consent is required under Section 7 of the Securities Act, as amended.

Exhibit 8.1

April 14, 2015

Atlas Resource Partners, L.P.

Park Place Corporate Center One

1000 Commerce Drive, Suite 400

Pittsburgh, PA 15275

Ladies and Gentlemen:

We have acted as counsel to Atlas Resource Partners, L.P. (the “Partnership”) in connection with its offer and sale of 255,000 of its 10.75% Class E cumulative redeemable perpetual preferred units representing limited partner interests (the “Offered Securities”), to be issued pursuant to the Partnership’s prospectus supplement dated April 7, 2015 and the base prospectus dated February 3, 2014 (collectively, the “Prospectus”), forming part of the Registration Statement on Form S-3 (Registration No. 333-193727) (the “Registration Statement”). You have requested our opinion regarding certain U.S. federal income tax matters. Capitalized terms not otherwise defined herein shall have the meaning set forth in that certain Underwriting Agreement dated April 7, 2015 by and among you and the underwriters named therein.

We are opining herein as to the effect on the subject transaction only of the federal income tax laws of the United States, and we express no opinion with respect to the applicability thereto, or the effect thereon, of other federal laws, foreign laws, the laws of any state or any other jurisdiction or as to any matters of municipal law or the laws of any other local agencies within any state. We hereby confirm that all statements of legal conclusions contained in the discussion in the Prospectus under the caption “Tax Considerations,” as supplemented by the discussion in the Prospectus Supplement under the caption “Material Tax Considerations,” constitute the opinion of Ledgewood, P.C. with respect to the matters set forth therein as of the effective date of the Registration Statement, subject to the assumptions, qualifications, and limitations set forth therein. No opinion is expressed as to any matter not discussed therein.

This opinion is rendered to you as of the effective date of the Registration Statement, and we undertake no obligation to update this opinion subsequent to the date hereof. This opinion is based on various statutory provisions, regulations promulgated thereunder and interpretations thereof by the Internal Revenue Service and the courts having jurisdiction over such matters, all of which are subject to change either prospectively or retroactively. Also, any variation or difference in the facts from those set forth in the representations described above, including in the Registration Statement, may affect the conclusions stated herein.

This opinion is furnished to you, and is for your use in connection with the transactions set forth in the Registration Statement. This opinion may not be relied upon by you for any other purpose or furnished to, assigned to, quoted to or relied upon by any other person, firm or other entity, for any purpose, without our prior written consent.

We hereby consent to the filing of this opinion of counsel as Exhibit 8.1 to the Current Report on Form 8-K of the Partnership dated on or about the date hereof, to the incorporation by reference of this opinion of counsel into the Registration Statement and to the reference to our firm in the Prospectus and the Prospectus Supplement. In giving such consent, we do not admit that we are within the category of persons whose consent is required under Section 7 of the Securities Act of 1933, as amended.