EXHIBIT 5.1
                                 -----------

                     [Letterhead of Thompson Coburn LLP]

Peabody Energy Corporation
701 Market Street
St. Louis, Missouri  63101-1826

Re:      Peabody Energy Corporation Deferred Compensation Plan

Ladies and Gentlemen:

         With reference to the Registration Statement on Form S-8 (the
"Registration Statement") being filed with the Securities and Exchange
Commission pursuant to the Securities Act of 1933, as amended, on December
13, 2001, by Peabody Energy Corporation, a Delaware corporation (the
"Company"), with respect to registering 100,000 stock units equivalent to
shares of the Company's common stock, $.01 par value (the "Units"), to be
credited to a participant's deferral account pursuant to the Peabody Energy
Corporation Deferred Compensation Plan (the "Plan"), we have examined such
corporate records of the Company, such laws and such other information as we
have deemed relevant, including the Company's Third Amended and Restated
Certificate of Incorporation, By-Laws, and resolutions adopted by the Board
of Directors of Peabody Energy Corporation relating to the Plan and offering
of the Units, the written documents constituting the Plan, certificates
received from state officials and statements we have received from officers
and representatives of the Company. In delivering this opinion, we have
assumed the genuineness of all signatures, the authenticity of all documents
submitted to us as originals, the conformity to the originals of all
documents submitted to us as certified, photostatic or conformed copies, the
authenticity of originals of all such latter documents, and the correctness
of statements submitted to us by officers and representatives of the
Company.

Based solely on the foregoing, we are of the opinion that:

1.       The Company is duly incorporated and is validly existing under the
         laws of the State of Delaware;

2.       The Plan and the Units to be credited to participants' deferral
         accounts by the Company have been duly authorized by the Company
         and, when credited to participants' deferral accounts by the
         Company in accordance with the Plan, the Units will be duly and
         validly issued and will represent the binding obligation of the
         Company, enforceable in accordance with the terms and conditions of
         the Plan, except as enforcement thereof may be limited by
         bankruptcy, garnishment or other creditors' rights; and

3.       The Plan is intended to qualify as an unfunded plan maintained by
         the Company primarily for the purpose of providing deferred
         compensation for a select group of management and highly
         compensated employees of the Company. Assuming such qualification,
         the Plan is exempt from the participation and vesting, funding and
         fiduciary responsibility requirements of the Employee Retirement
         Income Security Act of 1974, as amended, and the provisions of the
         Plan have been drafted to comply with this exemption.

         We consent to the filing of this opinion as an exhibit to the
Registration Statement. We further consent to the filing of copies of this
opinion with agencies of such states and other jurisdictions as you deem
necessary in the course of complying with the laws of the states and
jurisdictions regarding the issuance of the Units in accordance with the
Plan.

                                     Very truly yours,

                                     /s/ Thompson Coburn LLP