EXHIIBT 4.22


              SIXTH SUPPLEMENTAL SENIOR SUBORDINATED NOTE INDENTURE

         SIXTH SUPPLEMENTAL SENIOR SUBORDINATED NOTE INDENTURE (this
"Supplemental Senior Subordinated Note Indenture"), dated as of February 11,
2002, among THOROUGHBRED GENERATING COMPANY, LLC, a Delaware limited liability
company (the "Guaranteeing Subsidiary"), a subsidiary of Peabody Energy
Corporation (formerly P&L Coal Holdings Corporation) (or its permitted
successor), a Delaware corporation (the "Company"), the Company, the other
Senior Subordinated Note Guarantors (as defined in the Senior Subordinated Note
Indenture referred to herein) and State Street Bank and Trust Company, as Senior
Subordinated Note Trustee under the Senior Subordinated Note Indenture referred
to below (the "Senior Subordinated Note Trustee").

                                   WITNESSETH

         WHEREAS, the Company has heretofore executed and delivered to the
Senior Subordinated Note Trustee a Senior Subordinated Note Indenture (the
"Senior Subordinated Note Indenture"), dated as of May 18, 1998 providing for
the issuance of an aggregate principal amount of up to $650.0 million of 9-5/8%
Senior Subordinated Notes due 2008 (the "Senior Subordinated Notes");

         WHEREAS, the Senior Subordinated Note Indenture provides that under
certain circumstances the Guaranteeing Subsidiary shall execute and deliver to
the Senior Subordinated Note Trustee a supplemental Senior Subordinated Note
Indenture pursuant to which the Guaranteeing Subsidiary shall unconditionally
guarantee all of the Company's Obligations under the Senior Subordinated Notes
and the Senior Subordinated Note Indenture on the terms and conditions set forth
herein (the "Subordinated Subsidiary Guarantee"); and

         WHEREAS, pursuant to Section 9.01 of the Senior Subordinated Note
Indenture, the Senior Subordinated Note Trustee is authorized to execute and
deliver this Supplemental Senior Subordinated Note Indenture.

         NOW THEREFORE, in consideration of the foregoing and for other good and
valuable consideration, the receipt of which is hereby acknowledged, the
Guaranteeing Subsidiary and the Senior Subordinated Note Trustee mutually
covenant and agree for the equal and ratable benefit of the Holders of the
Senior Subordinated Notes as follows:

         1.       CAPITALIZED TERMS. Capitalized terms used herein without
definition shall have the meanings assigned to them in the Senior Subordinated
Note Indenture.

         2.       AGREEMENT TO GUARANTEE. The Guaranteeing Subsidiary hereby
agrees as follows:



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                  (a)      Along with all Senior Subordinated Note Guarantors
                           named in the Senior Subordinated Note Indenture, to
                           jointly and severally Guarantee to each Holder of a
                           Senior Subordinated Note authenticated and delivered
                           by the Senior Subordinated Note Trustee and to the
                           Senior Subordinated Note Trustee and its successors
                           and assigns, irrespective of the validity and
                           enforceability of the Senior Subordinated Note
                           Indenture, the Senior Subordinated Notes or the
                           obligations of the Company hereunder or thereunder,
                           that:

                           (i)      the principal of and interest on the Senior
                                    Subordinated Notes will be promptly paid in
                                    full when due, whether at maturity, by
                                    acceleration, redemption or otherwise, and
                                    interest on the overdue principal of and
                                    interest on the Senior Subordinated Notes,
                                    if any, if lawful, and all other obligations
                                    of the Company to the Holders or the Senior
                                    Subordinated Note Trustee hereunder or
                                    thereunder will be promptly paid in full or
                                    performed, all in accordance with the terms
                                    hereof and thereof; and

                           (ii)     in case of any extension of time of payment
                                    or renewal of any Senior Subordinated Notes
                                    or any of such other obligations, that same
                                    will be promptly paid in full when due or
                                    performed in accordance with the terms of
                                    the extension or renewal, whether at stated
                                    maturity, by acceleration or otherwise.
                                    Failing payment when due of any amount so
                                    guaranteed or any performance so guaranteed
                                    for whatever reason, the Senior Subordinated
                                    Note Guarantors shall be jointly and
                                    severally obligated to pay the same
                                    immediately.

                  (b)      Notwithstanding the foregoing, it is agreed and
                           acknowledged that the Subordinated Subsidiary
                           Guarantee hereunder is subordinated to the Senior
                           Debt of such Subordinated Senior Note Guarantor as
                           set forth in Article 10 and in Article 11 of the
                           Senior Subordinated Note Indenture.

                  (c)      The obligations hereunder shall be unconditional,
                           irrespective of the validity, regularity or
                           enforceability of the Senior Subordinated Notes or
                           the Senior Subordinated Note Indenture, the absence
                           of any action to enforce the same, any waiver or
                           consent by any Holder of the Senior Subordinated
                           Notes with respect to any provisions hereof or
                           thereof, the recovery of any judgment against the
                           Company, any action to enforce the same or any other
                           circumstance which might otherwise constitute a legal
                           or equitable discharge or defense of a Senior
                           Subordinated Note Guarantor.

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                  (d)      The following is hereby waived: diligence,
                           presentment, demand of payment, filing of claims with
                           a court in the event of insolvency or bankruptcy of
                           the Company, any right to require a proceeding first
                           against the Company, protest, notice and all demands
                           whatsoever.

                  (e)      This Subordinated Subsidiary Guarantee shall not be
                           discharged except by complete performance of the
                           obligations contained in the Senior Subordinated
                           Notes and the Senior Subordinated Note Indenture.

                  (f)      If any Holder or the Senior Subordinated Note Trustee
                           is required by any court or otherwise to return to
                           the Company, the Senior Subordinated Note Guarantors,
                           or any custodian, Senior Subordinated Note Trustee,
                           liquidator or other similar official acting in
                           relation to either the Company or the Senior
                           Subordinated Note Guarantors, any amount paid by
                           either to the Senior Subordinated Note Trustee or
                           such Holder, this Subordinated Subsidiary Guarantee,
                           to the extent theretofore discharged, shall be
                           reinstated in full force and effect.

                  (g)      The Guaranteeing Subsidiary shall not be entitled to
                           any right of subrogation in relation to the Holders
                           in respect of any obligations guaranteed hereby until
                           payment in full of all obligations guaranteed hereby.

                  (h)      As between the Senior Subordinated Note Guarantors,
                           on the one hand, and the Holders and the Senior
                           Subordinated Note Trustee, on the other hand, (x) the
                           maturity of the obligations guaranteed hereby may be
                           accelerated as provided in Article 6 of the Senior
                           Subordinated Note Indenture for the purposes of this
                           Subordinated Subsidiary Guarantee, notwithstanding
                           any stay, injunction or other prohibition preventing
                           such acceleration in respect of the obligations
                           guaranteed hereby, and (y) in the event of any
                           declaration of acceleration of such obligations as
                           provided in Article 6 of the Senior Subordinated Note
                           Indenture, such obligations (whether or not due and
                           payable) shall forthwith become due and payable by
                           the Senior Subordinated Note Guarantors for the
                           purpose of this Subordinated Subsidiary Guarantee.

                  (i)      The Senior Subordinated Note Guarantors shall have
                           the right to seek contribution from any non-paying
                           Senior Subordinated Note Guarantor so long as the
                           exercise of such right does not impair the rights of
                           the Holders under the Subordinated Subsidiary
                           Guarantee.



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                  (j)      Pursuant to Section 11.02 of the Senior Subordinated
                           Note Indenture, after giving effect to any maximum
                           amount and any other contingent and fixed liabilities
                           that are relevant under any applicable Bankruptcy or
                           fraudulent conveyance laws, and after giving effect
                           to any collections from, rights to receive
                           contribution from or payments made by or on behalf of
                           any other Senior Subordinated Note Guarantor in
                           respect of the obligations of such other Senior
                           Subordinated Note Guarantor under Article 11 of the
                           Senior Subordinated Note Indenture shall result in
                           the obligations of such Senior Subordinated Note
                           Guarantor under its Subordinated Subsidiary Guarantee
                           not constituting a fraudulent transfer or conveyance.

         3.       EXECUTION AND DELIVERY. Each Guaranteeing Subsidiary agrees
that the Subordinated Subsidiary Guarantees shall remain in full force and
effect notwithstanding any failure to endorse on each Senior Subordinated Note a
notation of such Subordinated Subsidiary Guarantee.

         4.       GUARANTEEING SUBSIDIARY MAY CONSOLIDATE, ETC. ON CERTAIN
TERMS.

                  (a)      The Guaranteeing Subsidiary may not consolidate with
                           or merge with or into (whether or not such Senior
                           Subordinated Note Guarantor is the surviving Person)
                           another corporation, Person or entity whether or not
                           affiliated with such Senior Subordinated Note
                           Guarantor unless:

                           (i)      subject to Section 11.05 of the Senior
                                    Subordinated Note Indenture, the Person
                                    formed by or surviving any such
                                    consolidation or merger (if other than a
                                    Senior Subordinated Note Guarantor or the
                                    Company) unconditionally assumes all the
                                    obligations of such Senior Subordinated Note
                                    Guarantor, pursuant to a supplemental Senior
                                    Subordinated Note Indenture in form and
                                    substance reasonably satisfactory to the
                                    Senior Subordinated Note Trustee, under the
                                    Senior Subordinated Notes, the Senior
                                    Subordinated Note Indenture and the
                                    Subordinated Subsidiary Guarantee on the
                                    terms set forth herein or therein; and

                           (ii)     immediately after giving effect to such
                                    transaction, no Default or Event of Default
                                    exists.

                  (b)      In case of any such consolidation, merger, sale or
                           conveyance and upon the assumption by the successor
                           corporation, by




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                           supplemental Senior Subordinated Note Indenture,
                           executed and delivered to the Senior Subordinated
                           Note Trustee and satisfactory in form to the Senior
                           Subordinated Note Trustee, of the Subordinated
                           Subsidiary Guarantee endorsed upon the Senior
                           Subordinated Notes and the due and punctual
                           performance of all of the covenants and conditions of
                           the Senior Subordinated Note Indenture to be
                           performed by the Senior Subordinated Note Guarantor,
                           such successor corporation shall succeed to and be
                           substituted for the Senior Subordinated Note
                           Guarantor with the same effect as if it had been
                           named herein as a Senior Subordinated Note Guarantor.
                           Such successor corporation thereupon may cause to be
                           signed any or all of the Subordinated Subsidiary
                           Guarantees to be endorsed upon all of the Senior
                           Subordinated Notes issuable hereunder which
                           theretofore shall not have been signed by the Company
                           and delivered to the Senior Subordinated Note
                           Trustee. All the Subordinated Subsidiary Guarantees
                           so issued shall in all respects have the same legal
                           rank and benefit under the Senior Subordinated Note
                           Indenture as the Subordinated Subsidiary Guarantees
                           theretofore and thereafter issued in accordance with
                           the terms of the Senior Subordinated Note Indenture
                           as though all of such Subordinated Subsidiary
                           Guarantees had been issued at the date of the
                           execution hereof.

                  (c)      Except as set forth in Articles 4 and 5 of the Senior
                           Subordinated Note Indenture, and notwithstanding
                           clauses (a) and (b) above, nothing contained in the
                           Senior Subordinated Note Indenture or in any of the
                           Senior Subordinated Notes shall prevent any
                           consolidation or merger of a Senior Subordinated Note
                           Guarantor with or into the Company or another Senior
                           Subordinated Note Guarantor, or shall prevent any
                           sale or conveyance of the property of a Senior
                           Subordinated Note Guarantor as an entirety or
                           substantially as an entirety to the Company or
                           another Senior Subordinated Note Guarantor.

         5.       RELEASES.

                  (a)      In the event of a sale or other disposition of all of
                           the assets of any Senior Subordinated Note Guarantor,
                           by way of merger, consolidation or otherwise, or a
                           sale or other disposition of all to the capital stock
                           of any Senior Subordinated Note Guarantor, then such
                           Senior Subordinated Note Guarantor (in the event of a
                           sale or other disposition, by way of merger,
                           consolidation or otherwise, of all of the capital
                           stock of such Senior Subordinated Note Guarantor) or
                           the corporation acquiring the property (in the event
                           of a sale or other disposition of all or
                           substantially all of the assets of such Senior
                           Subordinated Note Guarantor) will be released and



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                           relieved of any obligations under its Subordinated
                           Subsidiary Guarantee; provided that the Net Proceeds
                           of such sale or other disposition are applied in
                           accordance with the applicable provisions of the
                           Senior Subordinated Note Indenture, including without
                           limitation Section 4.10 of the Senior Subordinated
                           Note Indenture. Upon delivery by the Company to the
                           Senior Subordinated Note Trustee of an Officer's
                           Certificate and an Opinion of Counsel to the effect
                           that such sale or other disposition was made by the
                           Company in accordance with the provisions of the
                           Senior Subordinated Note Indenture, including without
                           limitation Section 4.10 of the Senior Subordinated
                           Note Indenture, the Senior Subordinated Note Trustee
                           shall execute any documents reasonably required in
                           order to evidence the release of any Senior
                           Subordinated Note Guarantor from its obligations
                           under its Subordinated Subsidiary Guarantee.

                  (b)      Any Senior Subordinated Note Guarantor not released
                           from its obligations under its Subordinated
                           Subsidiary Guarantee shall remain liable for the full
                           amount of principal of and interest on the Senior
                           Subordinated Notes and for the other obligations of
                           any Senior Subordinated Note Guarantor under the
                           Senior Subordinated Note Indenture as provided in
                           Article 11 of the Senior Subordinated Note Indenture.

         6.       NO RECOURSE AGAINST OTHERS. No past, present or future
director, officer, employee, incorporator, stockholder or agent of the
Guaranteeing Subsidiary, as such, shall have any liability for any obligations
of the Company or any Guaranteeing Subsidiary under the Senior Subordinated
Notes, any Subordinated Subsidiary Guarantees, the Senior Subordinated Note
Indenture or this Supplemental Senior Subordinated Note Indenture or for any
claim based on, in respect of, or by reason of, such obligations or their
creation. Each Holder of the Senior Subordinated Notes by accepting a Senior
Subordinated Note waives and releases all such liability. The waiver and release
are part of the consideration for issuance of the Senior Subordinated Notes.
Such waiver may not be effective to waive liabilities under the federal
securities laws and it is the view of the Commission that such a waiver is
against public policy.

         7.       NEW YORK LAW TO GOVERN. THE INTERNAL LAW OF THE STATE OF NEW
YORK SHALL GOVERN AND BE USED TO CONSTRUE THIS SUPPLEMENTAL SENIOR SUBORDINATED
NOTE INDENTURE BUT WITHOUT GIVING EFFECT TO APPLICABLE PRINCIPLES OF CONFLICTS
OF LAW TO THE EXTENT THAT THE APPLICATION OF THE LAWS OF ANOTHER JURISDICTION
WOULD BE REQUIRED THEREBY.

         8.       COUNTERPARTS. The parties may sign any number of copies of
this Supplemental Senior Subordinated Note Indenture. Each signed copy shall be
an original, but all of them together represent the same agreement.



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         9.       EFFECT OF HEADINGS. The Section headings herein are for
convenience only and shall not affect the construction hereof.

         10.      THE SENIOR SUBORDINATED NOTE TRUSTEE. The Senior Subordinated
Note Trustee shall not be responsible in any manner whatsoever for or in respect
of the validity or sufficiency of this Supplemental Senior Subordinated Note
Indenture or for or in respect of the recitals contained herein, all of which
recitals are made solely by the Guaranteeing Subsidiary and the Company.

         IN WITNESS WHEREOF, the parties hereto have caused this Supplemental
Senior Subordinated Note Indenture to be duly executed and attested, all as of
the date first above written.

                                         THOROUGHBRED GENERATING COMPANY, LLC


                                           By: /s/ Steven F. Schaab
                                              --------------------
                                           Name:  S. F. Schaab
                                           Title:  Vice President & Treasurer






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