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): November 22, 2016 (November 21, 2016)

ULTRA PETROLEUM CORP.

(Exact name of registrant as specified in its charter)

400 North Sam Houston Parkway East, Suite 1200

Houston, Texas 77060

(Address of principal executive offices, including zip code)

Registrant’s telephone number, including area code: (281) 876-0120

(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:

On November 21, 2016, Ultra Petroleum Corp. (“UPL”) and its subsidiaries UP Energy Corporation, Ultra Resources, Inc., Keystone Gas Gathering, LLC, Ultra Wyoming, Inc., Ultra Wyoming LGS, LLC, UPL Pinedale, LLC, UPL Three Rivers Holdings, LLC (collectively, with UPL, the “Ultra Entities”) entered into:

Plan Support Agreement

The Plan Support Agreement sets forth the agreement among the Ultra Entities and the Plan Support Parties to seek and support a proposed joint plan of reorganization for the Ultra Entities (the “Plan”) on and subject to the terms and conditions set forth therein (as previously reported, on April 29, 2016, the Ultra Entities filed voluntary petitions for reorganization under chapter 11 of the United States Bankruptcy Code (the “Code”) in the United States Bankruptcy Court for the Southern District of Texas (the “Court”); the petitions are being jointly administered under the caption In re Ultra Petroleum Corp., et al, Case No. 16-32202 (the “Ultra Proceedings”)). The Plan Support Agreement includes a term sheet detailing the terms and conditions of the Plan (the “Term Sheet”). The Backstop Agreement details the terms and conditions on which the Commitment Parties have agreed to fund an offering of rights to purchase shares of common stock in UPL in connection with the Plan (the “Rights Offering”).

Certain provisions, terms and conditions set forth in the Plan Support Agreement and the Term Sheet are outlined below:

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Backstop Agreement

Pursuant to the Backstop Agreement, the Commitment Parties have agreed to backstop the Rights Offering to be conducted in accordance with the Plan. In accordance with the Plan, the Backstop Agreement and certain Rights Offering procedures to be filed as part of the Plan, UPL will offer eligible debt and equity holders, including the Commitment Parties, the right to purchase shares of new common stock in UPL upon effectiveness of the Plan for an aggregate purchase price of $580.0 million. The Rights Offering will consist of the following offerings:

Under the Backstop Agreement, certain Commitment Parties have agreed to purchase the HoldCo Noteholder Rights Offering Shares and the HoldCo Equityholder Rights Offering Shares, as applicable, that are not duly subscribed for pursuant to the HoldCo Noteholder Rights Offering or the HoldCo Equityholder Rights Offering, as applicable, by parties other than Commitment Parties (the “Backstop Commitment”) at the Rights Offering Price.

The Ultra Entities will pay the Commitment Parties upon the closing of the Rights Offering a Commitment Premium equal to 6.0% of the $580.0 million committed amount (the “Commitment Premium”). The Commitment Premium shall be fully earned as of the date of the Approval Order (as defined in the Plan Support Agreement). If the Approval Order is entered, the Commitment Premium will be paid either in the form of new common stock at the Rights Offering Price, if the Plan is consummated as contemplated in the Plan Support Agreement, or in cash in the amount of 4.0% of the $580.0 million committed amount, if the Backstop Agreement is terminated under certain circumstances other than, for example, a material breach by

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the Commitment Parties. All amounts payable to the Commitment Parties in their capacities as such for the Commitment Premium shall be paid pro rata based on the amount of their respective backstop commitments on the Plan effective date (as compared to the aggregate backstop commitment of all Commitment Parties). However, the Commitment Premium shall not be paid to any Commitment Party that has defaulted with respect to its respective backstop commitment or is otherwise in breach of the Backstop Agreement in any material respect.

The rights to purchase new common stock in the Rights Offering, any shares issued upon exercise thereof, and all shares issued to the Commitment Parties in respect of their backstop commitments pursuant to the Commitment Premium, will be issued (i) pursuant to an effective registration statement under the Securities Act of 1933, as amended (the “Securities Act”), or (ii) in reliance upon the exemption from the registration requirements of the securities laws pursuant to Section 1145 of the Bankruptcy Code. All shares issued to the Commitment Parties pursuant to the Backstop Agreement in respect of their Backstop Commitment will be issued (i) pursuant to an effective registration statement under the Securities Act or (ii) in reliance upon the exemption from registration under the Securities Act, provided by Section 4(a)(2) thereof and/or Regulation D thereunder. As a condition to the closing of the transactions contemplated by the Backstop Agreement and the Term Sheet, UPL will enter into a registration rights agreement with the Commitment Parties entitling such Commitment Parties to request that UPL register their restricted securities for sale under the Securities Act at various times.

The Commitment Parties’ commitments to backstop the Rights Offering, and the other transactions contemplated by the Backstop Agreement and the Term Sheet, are conditioned upon the satisfaction of all conditions to the effectiveness of the Plan, and other applicable conditions precedent set forth in the Backstop Agreement and the Term Sheet, including the entry of the Approval Order and the execution and delivery of the Backstop Agreement. The issuances of new common stock pursuant to the Rights Offering and the Backstop Agreement are conditioned upon, among other things, confirmation of the Plan by the Court, and the Plan’s effectiveness.

The foregoing descriptions of the Plan Support Agreement, the Term Sheet, and the Backstop Agreement are summary only and are qualified in their respective entireties by reference to the complete text of the applicable documents, copies of which are attached as exhibits to this Current Report on Form 8-K and incorporated herein by reference. Please see Item 9.01 below and the attached exhibits.

Press Release

On November 22, 2016, UPL issued a press release announcing its entry into the Plan Support Agreement and the Backstop Agreement, as described above in Item 1.01. The press release is attached hereto as Exhibit 99.1 to this Current Report on Form 8-K. Please see Item 9.01 below and the attached exhibit.

The information included in this Current Report on Form 8-K under Item 7.01 and Exhibit 99.1 is being furnished and shall not be deemed “filed” for purposes of Section 18 of the Securities Exchange Act of 1934, as amended (the “Exchange Act”), or otherwise subject to liabilities of that Section, unless the registrant specifically states that the information is to be considered “filed” under the Exchange Act or incorporates it by reference into a filing under the Exchange Act or the Securities Act of 1933, as amended.

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Confidentiality Agreement Disclosures

Prior to execution of the Plan Support Agreement, UPL entered into certain Confidentiality and Non-Disclosure Agreements with the Plan Support Parties (collectively, as amended, the “Confidentiality Agreements”). Pursuant to the Confidentiality Agreements, UPL agreed to publicly disclose all material non-public information regarding the Ultra Entities that was provided to the Plan Support Parties (the “Cleansing Materials”), including the Term Sheet, the Backstop Agreement and certain other information the legal and financial advisors for the Plan Support Parties asked UPL to disclose.

Copies of the Cleansing Materials are attached as Exhibit 99.2 to this Current Report on Form 8-K. Please see Item 9.01 below and the attached exhibits.

Portions of the financial projections, forecasts, oil and gas reserve estimates and other information included in the Cleansing Materials were not prepared with a view toward public disclosure or compliance with the published guidelines of the U.S. Securities and Exchange Commission or the guidelines established by the American Institute of Certified Public Accountants regarding financial projections or forecasts or oil and gas reserve estimates. Any such projections do not purport to present the estimated value or financial condition of any of the Ultra Entities in accordance with U.S. generally accepted accounting principles. The inclusion of any such projections or estimates in the Cleansing Materials should not be relied upon as such. In addition, the format of portions of the Cleansing Materials were determined by the professional advisors of the Plan Support Parties, not by the Ultra Entities. Neither any of the Ultra Entities nor any of their representatives undertakes any obligation to publicly update or correct any of the projections, forecasts, estimates or other information included in the Cleansing Materials, even if any or all of the assumptions underlying such projections, forecasts, estimates or other information prove to have been incorrect.

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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.

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EXHIBIT INDEX

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