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): October 30, 2012

Patriot Coal Corporation

(Exact name of registrant as specified in its charter)

Registrant’s telephone number, including area code: (314) 275-3600

Not Applicable

(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 7.01. Regulation FD Disclosure.

As previously reported, on July 9, 2012, Patriot Coal Corporation (the “Company”) and certain of its wholly owned subsidiaries (together with the Company, the “Debtors”) filed voluntary petitions for reorganization (the “Chapter 11 Petitions”) under Chapter 11 of the U.S. Code (the “Bankruptcy Code”) in the Bankruptcy Court for the Southern District of New York (the “Bankruptcy Court”). The Company’s joint ventures and certain of its other subsidiaries (the “non-Debtors”) were not included in the Chapter 11 Petitions.

On October 30, 2012, the Debtors filed their monthly operating report for the period ended September 30, 2012 (the “Monthly Operating Report”) with the Bankruptcy Court. The Monthly Operating Report is attached hereto as Exhibit 99.1 and is incorporated herein by reference. This current report (including the exhibit hereto or any information included therein) shall not be deemed an admission as to the materiality of any information required to be disclosed solely by reason of Regulation FD.

The Monthly Operating Report has been prepared on a consolidated basis for the Debtors. The information furnished in the Monthly Operating Report includes primarily normal recurring adjustments but not all the adjustments that would typically be made for the quarterly and annual consolidated financial statements to be in accordance with U.S. generally accepted accounting principles (“GAAP”).

The Company is furnishing this Form 8-K pursuant to Item 7.01, “Regulation FD Disclosure.” The information contained in this current report 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 the liabilities of that section, nor shall it be deemed 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.

FINANCIAL AND OPERATING DATA

The Company cautions investors and potential investors not to place undue reliance upon the information contained in the Monthly Operating Report, which was not prepared for the purpose of providing the basis for an investment decision relating to any of the securities of the Company. The Company cannot predict what the ultimate value of any of its securities may be and it remains too early to determine whether holders of any such securities will receive any distribution in the Debtors’ reorganization. In particular, in most cases under Chapter 11 of the Bankruptcy Code, holders of equity securities receive little or no recovery of value from their investment. The Monthly Operating Report is limited in scope, covers a limited time period and has been prepared solely for the purpose of complying with the monthly reporting requirements of the Office of the United States Trustee of the Southern District of New York and the Bankruptcy Court. The Monthly Operating Report was not audited or reviewed by independent accountants, is in a format prescribed by applicable bankruptcy laws and regulations and is subject to future adjustment and reconciliation. The Monthly Operating Report does not include all of the information and footnotes required by GAAP. Therefore, the Monthly Operating Report does not necessarily contain all information required in filings pursuant to the Exchange Act, or may present such information differently from such requirements. There can be no assurance that, from the perspective of an investor or potential investor in the Company’s securities, the Monthly Operating Report is complete. The Monthly Operating Report also contains information for periods which are shorter or otherwise different from those required in the Company’s filings pursuant to the Exchange Act, and such information might not be indicative of the Company’s financial condition or operating results for the period that would be reflected in the Company’s financial statements or in its reports pursuant to the Exchange Act. Results set forth in the Monthly Operating Report should not be viewed as indicative of future results.

FORWARD-LOOKING STATEMENTS

This current report on Form 8-K and the exhibit hereto contain forward-looking statements. Actual results may differ materially from the results suggested by these forward-looking statements. Readers are referred to the documents filed by the Company with the Securities and Exchange Commission, which further identify the important risk factors that could cause actual results to differ materially from the forward-looking statements in this current report on Form 8-K and the exhibit hereto. The Company disclaims any obligations to update any forward-looking statements.

Item 9.01. Financial Statements and Exhibits.

(d) Exhibits

The following exhibit relating to Item 7.01 shall be deemed to be furnished, and not filed:

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.

Dated: October 30, 2012

EXHIBIT INDEX