<PAGE>
                                                                     EXHIBIT 4.1

                       THIRD AMENDMENT TO CREDIT AGREEMENT


         THIS THIRD AMENDMENT TO CREDIT AGREEMENT (the "Amendment"), dated and
effective as of August 19, 2003, is made by and among ARCH COAL, INC., a
Delaware corporation (the "Borrower"), the LENDERS (as hereinafter defined),
JPMORGAN CHASE BANK, in its capacity as syndication agent, CITIBANK, N.A.,
CREDIT LYONNAIS NEW YORK BRANCH and U.S. BANK NATIONAL ASSOCIATION, each in its
capacity as a documentation agent, and PNC BANK, NATIONAL ASSOCIATION, in its
capacity as administrative agent for the Lenders (hereinafter referred to in
such capacity as the "Administrative Agent").

                              W I T N E S S E T H:

         WHEREAS, the Borrower, JPMorgan Chase Bank (successor in such capacity
to Morgan Guaranty Trust Company of New York), as syndication agent, Wachovia
Corporation (successor in such capacity to First Union National Bank), as
documentation agent, PNC Bank, National Association, as administrative agent,
and certain lenders are parties to that Credit Agreement dated as of June 1,
1998, as amended as of January 21, 2000, as amended and restated as of April 18,
2002, and as further amended as of January 27, 2003 and June 25, 2003 (the
"Original Credit Agreement");

         WHEREAS, the Borrower proposes to consummate certain transactions,
otherwise referred to as the Vulcan Acquisition (as hereinafter defined), as
contemplated by and subject to the terms and conditions of the Vulcan Merger
Agreement (as hereinafter defined); and

         WHEREAS, subject to the terms and conditions hereinafter provided and
effective upon the consummation of the Vulcan Acquisition, the parties desire to
amend and restate the Original Credit Agreement as hereinafter provided.

         NOW, THEREFORE, the parties hereto, in consideration of their mutual
covenants and agreements hereinafter set forth and intending to be legally bound
hereby, covenant and agree as follows:

         1. Recitals.

         The foregoing recitals are true and correct and incorporated herein by
reference.

         2. Definitions.

         The following words and terms shall have the following meanings,
respectively:

                  Amended and Restated Credit Agreement shall mean that certain
Amended and Restated Credit Agreement attached hereto as Exhibit A.



<PAGE>

                  Vulcan Acquisition shall mean the transactions contemplated by
the Vulcan Merger Agreement.

                  Vulcan Merger Agreement shall mean that certain Merger and
Purchase Agreement among Borrower, Triton Acquisition LLC, a Delaware limited
liability company, New Vulcan Holdings, L.L.C., a Delaware limited liability
company and Vulcan Coal Holdings, L.L.C., a Delaware limited liability company,
dated as of May 29, 2003, together with all schedules and exhibits thereto.

                  All other capitalized terms used herein unless otherwise
defined herein shall have the meanings ascribed to them in the Original Credit
Agreement.

         3. Amendment and Restatement of Original Credit Agreement.

         The Amended and Restated Credit Agreement shall become effective and
shall automatically amend and restate the Original Credit Agreement, without
further action, upon the date of the satisfaction of all conditions set forth in
Section 6.1 of the Amended and Restated Credit Agreement, which conditions
(including all definitions and sections of the Amended and Restated Credit
Agreement that are referred to in such Section 6.1) are expressly incorporated
herein by reference and made a part hereof (collectively, the "Restatement
Closing Conditions").

         It is expressly agreed that any amendment to any of the Restatement
Closing Conditions or any waiver of any of the Restatement Closing Conditions
shall require the prior written approval of the Required Banks and of the
Borrower, which approval shall be binding on all of the Banks.

         4. Amendment to Original Credit Agreement.

         Clauses (v) and (vi) of Section 7.2.4 [Disposition of Assets or
Subsidiaries] of the Original Credit Agreement are hereby amended and restated
in their entirety to read as follows:

                  "(v) any sale, transfer or lease (including any lease
                  transaction under Section 7.2.9 [Off-Balance Sheet Financing
                  and Capital Leases]) of assets, other than those specifically
                  excepted pursuant to clauses (i) through (iv) above or clauses
                  (vi), (vii), (viii), (ix) or (x) below, provided that any
                  disposition of assets by Borrower after the consummation of
                  the MLP Transaction to the master limited partnership or
                  similar entity formed in connection with the MLP Transaction
                  shall be subject to and governed by solely this clause (v),
                  provided further that with respect to any sale, transfer or
                  lease pursuant to this Section 7.2.4(v): (a) at the time of
                  any such disposition, no Event of Default shall exist or shall
                  result from such disposition, (b) the Borrower and its
                  Subsidiaries shall be in compliance with the covenants
                  contained in Sections 7.2.10 [Maximum Leverage Ratio], 7.2.11
                  [Minimum Fixed Charge Coverage Ratio], and 7.2.12 [Minimum Net
                  Worth] determined on a pro forma basis after giving effect to
                  each such sale, transfer or lease of assets, and (c) the
                  aggregate net book

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<PAGE>

                  value, as determined in accordance with GAAP, of all assets so
                  sold, transferred, or leased by the Borrower and its
                  Subsidiaries shall not exceed in any calendar year
                  $40,000,000;

                  (vi) subject to the first proviso of clause (v) above, any
                  sale, transfer or lease of assets, other than those
                  specifically excepted pursuant to clauses (i) through (v)
                  above or clauses (vii), (viii), (ix) or (x), below, so long as
                  (y) in the case of any such permitted transaction by any
                  member of the Arch Coal Group, a permanent reduction of the
                  Revolving Credit Commitments with respect to the Net Cash
                  Proceeds thereof is made in accordance with the provisions of
                  Section 4.4.5, and (z) in the case of any such permitted
                  transaction by any member of the Arch Western Group, the
                  mandatory payments and/or redemptions of the Indebtedness of
                  Arch Western or the applicable Subsidiary of Arch Western are
                  made in accordance with Section 4.09 of the AWR Senior Notes
                  Indenture or the mandatory redemptions of other Permitted
                  Additional AWR Indebtedness are made in accordance with the
                  indenture or agreement to which such Permitted Additional AWR
                  Indebtedness is subject;"

         5. Conditions of Effectiveness of this Amendment.

         The effectiveness of this Amendment is expressly conditioned upon
satisfaction of each of the following conditions precedent:

         (a) Fees and Expenses. The Borrower shall pay or cause to be paid, on
the Third Amendment Effective Date (as hereinafter defined) all fees and
expenses set forth in that certain agreement among the Borrower, the
Administrative Agent and PNC Capital Markets, Inc., regarding fees payable in
connection with this Amendment, including, without limitation: (i) to the
Administrative Agent for itself the reasonable costs and expenses of the
Administrative Agent including, without limitation, reasonable fees of the
Administrative Agent's counsel in connection with this Amendment, and (ii) to
the Administrative Agent for the benefit of each Lender approving this Amendment
on or prior to the Third Amendment Effective Date, a fee equal to 18.75 basis
points of each such Lender's Revolving Credit Commitment as of the Third
Amendment Effective Date.

         (b) No Default. Confirmation of Representations and Warranties, etc. As
of the Third Amendment Effective Date after giving effect to this Amendment, no
Event of Default or Potential Default shall have occurred. The Borrower by
executing this Amendment hereby certifies and confirms that as of the date
hereof and after giving effect to this Amendment: (a) the execution, delivery
and performance of this Amendment and any and all other documents executed
and/or delivered in connection herewith have been authorized by all requisite
corporate action on the part of the Borrower and will not violate the Borrower's
articles of incorporation or bylaws, (b) no Event of Default or Potential Event
of Default has occurred or would result from the execution, delivery and
performance of this Amendment, (c) the representations and warranties of the
Loan Parties contained in the Original Credit Agreement and the other Loan
Documents are true and correct on and as of the date hereof with the same force
and effect as


                                       3
<PAGE>

though made by the Loan Parties on such date (except representations and
warranties that relate solely to an earlier date or time), and (d) the Original
Credit Agreement (as amended by this Amendment) and all other Loan Documents are
and remain legal, valid, binding and enforceable obligations in accordance with
the terms thereof.

         (c) Confirmation of Loan Documents. Each Loan Party (other than the
Borrower) shall have duly executed and delivered to the Administrative Agent the
Confirmation of Loan Documents in the form attached hereto as Exhibit B.

         (d) Organization, Authorization and Incumbency. There shall be
delivered to the Administrative Agent for the benefit of each Lender a
certificate, dated as of the date hereof and signed by the Secretary or an
Assistant Secretary of each Loan Party, certifying as appropriate as to:

                  (i) all action taken by such Loan Party in connection with
         this Amendment and the other Loan Documents;

                  (ii) the names of the officer or officers authorized to sign
         this Amendment and the other documents executed and delivered in
         connection herewith and described in this Section 5 and the true
         signatures of such officer or officers and specifying the officers
         authorized to act on behalf of each Loan Party for purposes of the Loan
         Documents and the true signatures of such officers, on which the Agents
         and each Lender may conclusively rely; and

                  (iii) copies of its organizational documents, including its
         certificate of incorporation and bylaws if it is a corporation, its
         certificate of partnership and partnership agreement if it is a
         partnership, and its certificate of organization and limited liability
         company operating agreement if it is a limited liability company, in
         each case as in effect on the date hereof, certified by the appropriate
         state official where such documents are filed in a state office
         together with certificates from the appropriate state officials as to
         the continued existence and good standing of each of the Loan Parties
         in each state where organized or qualified to do business; provided
         that each of the Loan Parties other than Borrower may, in lieu of
         delivering copies of the foregoing organizational documents and good
         standing certificates, certify that the organizational documents and
         good standing certificates previously delivered by the Loan Parties to
         the Administrative Agent remain in full force and effect and have not
         been modified, amended or rescinded.

         (e) Consents and Approvals. To the extent any consent, approval, order,
or authorization or registration, declaration, or filing with any governmental
authority or other person or legal entity is required in connection with the
valid execution and delivery of this Amendment or the carrying out or
performance of any of the transactions required or contemplated by this
Amendment, all such consents, approvals, orders or authorizations shall have
been obtained or all such registrations, declarations, or filings shall have
been accomplished prior to the consummation of this Amendment.


                                       4
<PAGE>

         (f) Litigation. Except as disclosed in the schedules to the Original
Credit Agreement, on the date hereof no action, proceeding, investigation,
regulation or legislation shall have been instituted, threatened or proposed
before any court, governmental agency or legislative body to enjoin, restrain or
prohibit, or to obtain damages in respect of, this Amendment or any other Loan
Documents or the consummation of the transactions contemplated hereby or thereby
or which, in the Administrative Agent's sole discretion, would make it
inadvisable to consummate the transactions contemplated by this Amendment or any
of the other Loan Documents.

         (g) Legal Details; Counterparts. All legal details and proceedings in
connection with the transactions contemplated by this Amendment shall be in form
and substance satisfactory to the Administrative Agent, the Administrative Agent
shall have received from the Borrower and the Lenders an executed original of
this Amendment and the Administrative Agent shall have received all such other
counterpart originals or certified or other copies of such documents and
proceedings in connection with such transactions, in form and substance
satisfactory to the Administrative Agent.

This Amendment shall be dated as of and shall become effective on the date that
(such date being hereinafter referred to as the "Third Amendment Effective
Date"): (i) it has been duly executed by the Borrower, the Administrative Agent
and the Required Banks, and (ii) each of the conditions set forth in this
Section 5 has been satisfied.

         6. Force and Effect.

         No novation is intended or shall occur by or as a result of this
Amendment. The Borrower reconfirms, restates, and ratifies the Original Credit
Agreement (as amended by this Amendment), each of the other Loan Documents and
all other documents executed in connection therewith, and the Borrower confirms
that all such documents have remained in full force and effect since the date of
their execution. This Amendment is not intended to constitute, nor does it
constitute, an interruption, suspension of continuity, satisfaction, discharge
of prior duties, novation, or termination of the liens, security interests,
indebtedness, loans, liabilities, expenses, or obligations under the Original
Credit Agreement or the other Loan Documents. The Borrower and the
Administrative Agent and each of the Lenders acknowledges and agrees that the
Collateral has continued to secure the indebtedness, loans, liabilities,
expenses, and obligations under the Original Credit Agreement since the date of
execution of each applicable Loan Document, and all liens and security interests
in the Collateral which were granted pursuant to any of the Loan Documents shall
remain in full force and effect from and after the date hereof.

         7. Opinions of Counsel.

         On or before August 19, 2003, there shall be delivered to the
Administrative Agent for the benefit of each Lender the opinion of legal counsel
to the Loan Parties, in form and substance reasonably satisfactory to the
Administrative Agent and its counsel as to the matters set forth on Exhibit C to
this Amendment and as to such other matters incident to such transactions as the
Administrative Agent may reasonably request.



                                       5
<PAGE>


         8. Governing Law.

         This Amendment shall be deemed to be a contract under the laws of the
Commonwealth of Pennsylvania and for all purposes shall be governed by and
construed and enforced in accordance with the internal laws of the Commonwealth
of Pennsylvania without regard to its conflict of laws principles.

         9. Counterparts.

         This Amendment may be signed in any number of counterparts each of
which shall be deemed an original, but all of which together shall constitute
one and the same instrument.


                         [SIGNATURES BEGIN ON NEXT PAGE]











                                       6
<PAGE>

                      [SIGNATURE PAGE TO THIRD AMENDMENT TO
                        ARCH COAL, INC. CREDIT AGREEMENT]


         IN WITNESS WHEREOF, the parties hereto, by their officers thereunto
duly authorized, have executed this Amendment as of the day and year first above
written.


ATTEST:                                ARCH COAL, INC.



                                       By:                                [Seal]
---------------------------------         --------------------------------
Janet L. Horgan                        Name:  Robert J. Messey
Assistant Secretary                    Title: Senior Vice President and Chief
                                              Financial Officer




<PAGE>

                      [SIGNATURE PAGE TO THIRD AMENDMENT TO
                        ARCH COAL, INC. CREDIT AGREEMENT]


                                       PNC BANK, NATIONAL ASSOCIATION,
                                       individually and as Administrative Agent


                                       By:
                                          --------------------------------------
                                       Name:
                                            ------------------------------------
                                       Title:
                                             -----------------------------------





<PAGE>

                      [SIGNATURE PAGE TO THIRD AMENDMENT TO
                        ARCH COAL, INC. CREDIT AGREEMENT]


                                       JPMORGAN CHASE BANK, individually and as
                                       Syndication Agent


                                       By:
                                          --------------------------------------
                                       Name:
                                            ------------------------------------
                                       Title:
                                             -----------------------------------




<PAGE>

                      [SIGNATURE PAGE TO THIRD AMENDMENT TO
                        ARCH COAL, INC. CREDIT AGREEMENT]


                                       CITIBANK, N.A., individually and as
                                       Documentation Agent


                                       By:
                                          --------------------------------------
                                       Name:
                                            ------------------------------------
                                       Title:
                                             -----------------------------------




<PAGE>

                      [SIGNATURE PAGE TO THIRD AMENDMENT TO
                        ARCH COAL, INC. CREDIT AGREEMENT]


                                       CREDIT LYONNAIS NEW YORK BRANCH,
                                       individually and as Documentation Agent


                                       By:
                                          --------------------------------------
                                       Name:
                                            ------------------------------------
                                       Title:
                                             -----------------------------------




<PAGE>

                      [SIGNATURE PAGE TO THIRD AMENDMENT TO
                        ARCH COAL, INC. CREDIT AGREEMENT]


                                       U.S. BANK NATIONAL ASSOCIATION,
                                       individually and as Documentation Agent


                                       By:
                                          --------------------------------------
                                       Name:
                                            ------------------------------------
                                       Title:
                                             -----------------------------------




<PAGE>

                      [SIGNATURE PAGE TO THIRD AMENDMENT TO
                        ARCH COAL, INC. CREDIT AGREEMENT]


                                       BANK LEUMI USA


                                       By:
                                          --------------------------------------
                                       Name:
                                            ------------------------------------
                                       Title:
                                             -----------------------------------





<PAGE>

                      [SIGNATURE PAGE TO THIRD AMENDMENT TO
                        ARCH COAL, INC. CREDIT AGREEMENT]


                                       BNP PARIBAS


                                       By:
                                          --------------------------------------
                                       Name:
                                            ------------------------------------
                                       Title:
                                             -----------------------------------



                                       By:
                                          --------------------------------------
                                       Name:
                                            ------------------------------------
                                       Title:
                                             -----------------------------------





<PAGE>

                      [SIGNATURE PAGE TO THIRD AMENDMENT TO
                        ARCH COAL, INC. CREDIT AGREEMENT]


                                       CREDIT INDUSTRIEL ET COMMERCIAL


                                       By:
                                          --------------------------------------
                                       Name:
                                            ------------------------------------
                                       Title:
                                             -----------------------------------



                                       By:
                                          --------------------------------------
                                       Name:
                                            ------------------------------------
                                       Title:
                                             -----------------------------------




<PAGE>

                      [SIGNATURE PAGE TO THIRD AMENDMENT TO
                        ARCH COAL, INC. CREDIT AGREEMENT]


                                       FLEET NATIONAL BANK


                                       By:
                                          --------------------------------------
                                       Name:
                                            ------------------------------------
                                       Title:
                                             -----------------------------------




<PAGE>

                      [SIGNATURE PAGE TO THIRD AMENDMENT TO
                        ARCH COAL, INC. CREDIT AGREEMENT]


                                       MIZUHO CORPORATE BANK, LIMITED


                                       By:
                                          --------------------------------------
                                       Name:
                                            ------------------------------------
                                       Title:
                                             -----------------------------------




<PAGE>

                      [SIGNATURE PAGE TO THIRD AMENDMENT TO
                        ARCH COAL, INC. CREDIT AGREEMENT]


                                       THE BANK OF NEW YORK


                                       By:
                                          --------------------------------------
                                       Name:
                                            ------------------------------------
                                       Title:
                                             -----------------------------------




<PAGE>

                      [SIGNATURE PAGE TO THIRD AMENDMENT TO
                        ARCH COAL, INC. CREDIT AGREEMENT]


                                       WACHOVIA BANK, NATIONAL ASSOCIATION


                                       By:
                                          --------------------------------------
                                       Name:
                                            ------------------------------------
                                       Title:
                                             -----------------------------------