HALLADOR ENERGY CO

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 30, 2026

Hallador Energy Company

(Exact name of registrant as specified in its charter)

1183 East Canvasback Drive, Terre Haute, Indiana 47802

(Address, including zip code, of principal executive offices)

Registrant’s telephone number, including area code: (812)299-2800

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:

Securities registered pursuant to Section 12(b) of the Act:

Indicate by check mark whether the registrant is an emerging growth company as defined in Rule 405 of the Securities Act of 1933 (§230.405 of this chapter) or Rule 12b-2 of the Securities Exchange Act of 1934 (§240.12b-2 of this chapter).

Emerging growth company☐

If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 13(a) of the Exchange Act.☐

On May 30, 2026, Hallador Energy Company (the “Company”) entered into an Asset Purchase Agreement (the “APA”) with Energy World Corporation Ltd., incorporated in Australia (“Seller”), to acquire approximately 460 MW of Siemens gas turbines, generators, a steam turbine, and ancillary equipment (the “Equipment”) for an aggregate purchase price of $350 million.

The foregoing description of the APA does not purport to be complete and is qualified in its entirety by reference to the full text of the APA, which is filed herewith as Exhibit 10.1.

On June 1, 2026, the Company issued a press release announcing the matters described in Item 1.01 of this Current Report on Form 8-K. A copy of the press release is furnished herewith as Exhibit 99.1.

The information furnished pursuant to Item 7.01 of this Current Report on Form 8-K, including Exhibit 99.1, shall not be deemed “filed” for purposes of Section 18 of the Securities Exchange Act of 1934, as amended, or otherwise subject to the liabilities of that section, and shall not be deemed incorporated by reference into any filing under the Securities Act of 1933, as amended, or the Securities Exchange Act of 1934, as amended, except as expressly set forth by specific reference in such filing.

(d) Exhibits.

10.1 Asset Purchase Agreement Dated as of May 30, 2026, by and between Energy World Corporation Ltd. and Hallador Energy Company

99.1 Press Release of Hallador Energy Company dated June 1, 2026.

104 Cover Page Interactive Data File (embedded within the Inline XBRL document).

SIGNATURE

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.