Exhibit 5.1
                          Simpson Thacher & Bartlett
                             425 Lexington Avenue
                           New York, New York 10017



                                   May 17, 2001

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

Ladies and Gentlemen:

          We have acted as counsel to Peabody Energy Corporation, a Delaware
corporation (the "Company"), in connection with the Registration Statement on
Form S-1 (the "Registration Statement") filed by the Company with the Securities
and Exchange Commission (the "Commission") under the Securities Act of 1933, as
amended (the "Act"), relating to the issuance by the Company of 15,000,000
shares of common stock par value $0.01 per share (together with any additional
shares of such stock that may be issued by the Company pursuant to Rule 462(b)
(as prescribed by the Commission pursuant to the Act) in connection with the
offering described in the Registration Statement, the "Shares").

          We have examined the Registration Statement and a form of the share
certificate which has been filed with the Commission as an exhibit to the
Registration Statement.  We also have examined the originals, or duplicates or
certified or conformed copies, of such records, agreements, instruments and
other documents and have made such other and further investigations as we have
deemed relevant and necessary in connection with the opinions expressed herein.
As to questions of fact material to this opinion, we have relied upon
certificates of public officials and of officers and representatives of the
Company.


Peabody Energy Corporation              -2-                     May 17, 2001



          In such examination, we have assumed the genuineness of all
signatures, the legal capacity of natural persons, the authenticity of all
documents submitted to us as originals, the conformity to original documents of
all documents submitted to us as duplicates or certified or conformed copies,
and the authenticity of the originals of such latter documents.

          Based upon the foregoing, and subject to the qualifications and
limitations stated herein, we are of the opinion that (1) when the Board of
Directors of the Company (the "Board") has taken all necessary corporate action
to authorize and approve the issuance of the Shares and (2) upon payment and
delivery in accordance with the applicable definitive underwriting agreement
approved by the Board, the Shares will be validly issued, fully paid and
nonassessable.

          We are members of the Bar of the State of New York, and we do not
express any opinion herein concerning any law other than the Delaware General
Corporation Law (including the statutory provisions, all applicable provisions
of the Delaware Constitution and reported judicial decisions interpreting the
foregoing).

          We hereby consent to the filing of this opinion letter as Exhibit 5.1
to the Registration Statement and to the use of our name under the caption
"Legal Matters" in the Prospectus included in the Registration Statement.

                                    Very truly yours,



                                    /s/ SIMPSON THACHER & BARTLETT