EXHIBIT 3.121

                          CERTIFICATE OF INCORPORATION

                                       OF

                           THOROUGHBRED MINING COMPANY

                                    * * * * *

         1. The name of the corporation is: THOROUGHBRED MINING COMPANY

         2. The address of Its registered office in the State of Delaware is
         Corporation Trust Center. 1209 Orange Street, in the City of
         Wilmington, County of New Castle The name of its registered agent at
         such address is The Corporation Trust Company.

         3. The nature of the business or purposes to be conducted or promoted
         is:

         4. The total number of shares of stock which the corporation shall have
         authority to Issue is: One Hundred (100 ) and the par value of each of
         such shares is:

         Dollars ($ 10.00 ) amounting in the aggregate to One Thousand Dollars
         and No Cents ($1,000.00).

         5. The name and mailing address of each incorporator is as follow:



NAME              MAILING ADDRESS
- ----              ---------------
               
Scott Sharp       1209 Orange Street
                  Wilmington, DE 19801


                  The name and mailing address of each person who is to serve as
         a director until the first annual meeting of the stockholders or until
         a successor is elected and qualified, is as follows:

                                                           STATE OF DELAWARE
                                                          SECRETARY OF STATE
                                                       DIVISION OF CORPORATIONS
                                                       FILED 04:00 PM 01/07/2002
                                                          020010301 - 3477608





       NAME        MAILING ADDRESS
       ----        ---------------
                
ROGER B. WALCOTT   701 Market Street
                   9th Floor
                   St. Louis, MO


                  6. The corporation is to have perpetual existence.

                  7. In furtherance and not in limitation of the powers
         conferred by statute, the board of directors is expressly authorized:

                  To make, alter or repeal the by-laws of the corporation.

                  To authorize and cause to be executed mortgages and liens upon
         the real and personal property of the corporation.

                  To set apart out of any of the funds of the corporation
         available for dividends a reserve or reserves for any proper purpose
         and to abolish any such reserve in the manner in which it was created.

                  To designate one or more committees, each committee to consist
         of one or more of the directors of the corporation. The board may
         designate one or more directors as alternate members of any committee,
         who may replace any absent or disqualified member at any meeting of the
         committee. The by-laws may provide that in the absence or
         disqualification of a member of a committee, the member or members
         present at any meeting and not disqualified from voting, whether or not
         such member or members constitute a quorum, may unanimously appoint
         another member of the board of directors to act at the meeting in the
         place of any such absent or disqualified member. Any such committee, to
         the



         extent provided in the resolution of the board of directors, or in the
         by-laws of the corporation, shall have and may exercise all the powers
         and authority of the board of directors in the management of the
         business and affairs of the corporation, and may authorize the seal of
         the corporation to be affixed to all papers which may require it; but
         no such committee shall have the power or authority in reference to the
         following matters: (i) approving or adopting, or recommending to the
         stockholders, any action or matter expressly required by the Delaware
         General Corporation Law to be submitted to stockholders for approval or
         (ii) adopting, amending or repealing any bylaw of the corporation.

                  When and as authorized by the stockholders in accordance with
         law, to sell, lease or exchange all or substantially all of the
         property and assets of the corporation, including its good will and its
         corporate franchises, upon such terms and conditions and for such
         consideration, which may consist in whole or in part of money or
         property including shares of stock in, and/or other securities of, any
         other corporation or corporations, as its board of directors shall deem
         expedient and for the best interests of the corporation.

                  8.       Elections of directors need not be by written ballot
         unless the bylaws of the corporation shall provide.

                  9.       The corporation reserves the right to amend, alter,
         change or repeal any provision contained in this Certificate of
         Incorporation, in the manner now or hereafter prescribed by statute,
         and all rights conferred upon stockholders herein are granted subject
         to this reservation.



                  10.      A director of the corporation shall not be personally
         liable to the corporation or its stockholders for monetary damages for
         breach of fiduciary duty as a director except for liability (i) for any
         breach of the director's duty of loyalty to the corporation or its
         stockholders, (ii) for acts or omissions not in good faith or which
         involve intentional misconduct or a knowing violation of law, (iii)
         under Section 174 of the Delaware General Corporation Law, or (iv) for
         any transaction from which the director derived any improper personal
         benefit.

                  WE, THE UNDERSIGNED, being each of the incorporators
         hereinbefore named, for the purpose of forming a corporation pursuant
         to the General Corporation Law of the State of Delaware, do make this
         Certificate, hereby declaring and certifying that this is our act and
         deed and the facts herein stated are true, and accordingly have
         hereunto set our hands this 7th day of January, 2002.

                                        /s/ Scott Sharp
                                        ----------------------------------------
                                            Scott Sharp Incorporator



                                                           STATE OF DELAWARE
                                                          SECRETARY OF STATE
                                                       DIVISION OF CORPORATIONS
                                                       FILED 09:00 AM 01/22/2002
                                                          020039287 - 3477608

                            CERTIFICATE OF AMENDMENT

                                       OF

                          CERTIFICATE OF INCORPORATION

                            BEFORE PAYMENT OF CAPITAL

                                       OF

                           THOROUGHBRED MINING COMPANY

         I, the undersigned, being the director of THOROUGHBRED MINING COMPANY,
         a corporation organized and existing under and by virtue of the General
         Corporation Law of the State of Delaware,

         DO HEREBY CERTIFY:

         FIRST: That Article 1 of the Certificate of Incorporation be and it
         hereby is amended to read as follows:

         "The name of the corporation is: PEABODY ENERGY INVESTMENTS, INC."

         SECOND: That the corporation has not received any payment for any of
         its stock.

         THIRD: That the amendment was duly adopted in accordance with the
         provisions of section 241 of the General Corporation Law of the State
         of Delaware.

         IN WITNESS WHEREOF, I have signed this certificate this 21st day of
         January, 2002.

                                                     /s/ Roger B. Walcott
                                                     ---------------------------
                                                           Roger B. Walcott, Jr.
                                                                        Director