<PAGE>

                                                                    EXHIBIT 4(c)

                      ELEVENTH AMENDMENT TO LOAN AGREEMENT

         THIS ELEVENTH AMENDMENT TO LOAN AGREEMENT (this "Eleventh Amendment")
is made and entered into as of the 16th day of March, 2004, by and among SERVICE
TRANSPORT COMPANY, a Texas corporation ("Service Transport Company"), ADAMS
RESOURCES EXPLORATION CORPORATION, a Delaware corporation ("Exploration"),
BUCKLEY MINING CORPORATION, a Kentucky corporation ("Buckley Mining"), CJC
LEASING, INC., a Kentucky corporation ("CJC"), CLASSIC COAL CORPORATION, a
Delaware corporation ("Classic Coal"), ADA MINING CORPORATION, a Texas
corporation ("Ada Mining"), ADA RESOURCES, INC., a Texas corporation ("Ada
Resources"), and BAYOU CITY PIPELINES, INC., a Texas corporation formerly known
as Bayou City Barge Lines, Inc. ("Bayou City"), each with offices and place of
business at 5 Post Oak Place, 4400 Post Oak Parkway, 27th Floor, Houston, Texas
77027 (Service Transport Company, Exploration, Buckley Mining, CJC, Classic
Coal, Ada Mining and Bayou City are hereinafter individually called a "Borrower"
and collectively called the "Borrowers"), and BANK OF AMERICA, N.A., a national
banking association (the "Lender"), successor in interest by merger to
NationsBank, N.A. ("NationsBank"), which had changed its name to Bank of
America, N.A., and which was the successor in interest by merger to NationsBank
of Texas, N.A. (the "Original Lender").

         WHEREAS, the Borrowers and Ada Crude Oil Company ("Ada Crude Oil")
(collectively referred to as the "Original Borrowers") and the Original Lender
entered into that certain Loan Agreement dated October 27, 1993, which Loan
Agreement was amended by that certain First Amendment to Loan Agreement dated
October 27, 1994 among the Original Borrowers and the Original Lender, that
certain Second Amendment to Loan Agreement dated December 29, 1995 among the
Original Borrowers and the Original Lender, that certain Third Amendment to Loan
Agreement dated January 27, 1997 among the Original Borrowers and the Original
Lender and that certain Fourth Amendment to Loan Agreement (the "Fourth
Amendment") dated September 30, 1997 among the Original Borrowers and the
Original Lender (as amended, the "Original Loan Agreement"); and

         WHEREAS, the Borrowers (other than Ada Resources) and NationsBank
entered into that certain Fifth Amendment to Loan Agreement dated February 2,
1999, and the Borrowers (other than Ada Resources) and Lender entered into that
certain Sixth Amendment to Loan Agreement dated October 29, 1999; and

         WHEREAS, the Borrowers and the Lender entered into that certain Seventh
Amendment to Loan Agreement dated March 22, 2000 (the "Seventh Amendment"), that
certain Eighth Amendment to Loan Agreement dated October 27, 2000 (the "Eighth
Amendment"), that certain Ninth Amendment to Loan Agreement dated March 21, 2002
(the "Ninth Amendment") and that certain Tenth Amendment to Loan Agreement dated
March 17, 2003 (the "Tenth Amendment") (the Original Loan Agreement, as amended
by the Fifth Amendment, the Sixth Amendment, the Seventh Amendment, the Eighth
Amendment, the Ninth Amendment and the Tenth Amendment, is referred to herein as
the "Loan Agreement"); and

         WHEREAS, due to the assignment of the assets and assumption of
liabilities of Ada Crude Oil, it is no longer a party under the Loan Agreement;
and

         WHEREAS, the Borrowers and the Lender desire to make certain amendments
to the terms and provisions of the Loan Agreement, as set forth herein.

         NOW, THEREFORE, FOR AND IN CONSIDERATION of the mutual covenants and
agreements contained herein, the parties hereto agree as follows:

                                      IV-5
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    1.   The first sentence of Section 1.3(a) of the Loan Agreement is deleted
         in its entirety, and the following is substituted in its place:

         The Lender, during the period from the date of the Eleventh Amendment
         through October 29, 2005, subject to the terms and conditions of this
         Agreement, agrees (i) to make loans to the Borrowers pursuant to a
         revolving credit and term loan facility up to but not in excess of the
         lesser of $10,000,000.00 or the amount of the Tranche A Borrowing Base
         and (ii) to make additional loans to the Borrowers pursuant to a
         revolving credit and term loan facility up to but not in excess of the
         lesser of $7,500,000.00 or the amount of the Tranche B Borrowing Base.

    2.   The fourth and fifth sentences of Section 1.3(b) of the Loan Agreement
         are deleted in their entirety, and the following is substituted in
         their place:

         Commencing October 31, 2005, a principal payment shall made on each
         Note on the last day of each October, January, April and July in an
         amount equal to one-eighth (1/8th) of the principal amount outstanding
         under such Note at the close of Lender's business on October 29, 2005.
         All unpaid principal and accrued and unpaid interest on the Notes shall
         be due and payable on or before October 29, 2007.

    3.   The Borrowers and Lender hereby agree that, from and after the date of
         this Eleventh Amendment, the Tranche A Borrowing Base shall be
         $5,000,000.00, until the time of the next redetermination thereof
         pursuant to the terms of the Loan Agreement.

    4.   The closing of the transactions contemplated by this Eleventh Amendment
         is subject to the satisfaction of the following conditions:

                  (a) All legal matters incident to the transactions herein
         contemplated shall be satisfactory to Gardere Wynne Sewell LLP, counsel
         to the Lender;

                  (b) The Lender shall have received a fully executed copy of
         this Eleventh Amendment and a Notice as to Written Agreement; and

                  (c) The Lender shall have received an executed copy of
         resolutions of the Board of Directors of each of the Borrowers and the
         Guarantor, in form and substance satisfactory to the Lender,
         authorizing the execution, delivery and performance of this Eleventh
         Amendment and all documents, instruments and certificates referred to
         herein.

    5.   Each of the Borrowers hereby reaffirms each of its representations,
         warranties, covenants and agreements set forth in the Loan Agreement
         with the same force and effect as if each were separately stated herein
         and made as of the date hereof. Except as amended hereby, the Loan
         Agreement shall remain unchanged, and the terms, conditions and
         covenants of the Loan Agreement shall continue and be binding upon the
         parties hereto.

    6.   Each of the Borrowers hereby agrees that its liability under any and
         all documents and instruments executed by it as security for the
         Indebtedness (including, without limitation, the Mortgages, the
         Security Agreements, the Collateral Assignment and the Pledges) shall
         not be reduced, altered, limited, lessened or in any way affected by
         the execution and delivery of this Eleventh Amendment or any of the
         instruments or documents referred to herein, except as specifically set
         forth herein or therein, that all of such documents and instruments are
         hereby renewed, extended, ratified, confirmed and carried forward by
         the Borrowers in all respects, that all of such documents and
         instruments shall remain in full force and effect and are and shall
         remain enforceable against the Borrowers in accordance with their terms
         and that all of such documents and instruments shall cover all
         indebtedness of the Borrowers to the Lender described in the Loan
         Agreement as amended hereby.

                                      IV-6
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    7.   Each of the terms defined in the Loan Agreement is used in this
         Eleventh Amendment with the same meaning, except as otherwise indicated
         in this Eleventh Amendment. Each of the terms defined in this Eleventh
         Amendment is used in the Loan Agreement with the same meaning, except
         as otherwise indicated in the Loan Agreement.

    8.   THIS ELEVENTH AMENDMENT SHALL BE DEEMED TO BE A CONTRACT UNDER, SUBJECT
         TO, AND SHALL BE CONSTRUED FOR ALL PURPOSES IN ACCORDANCE WITH THE LAWS
         OF THE STATE OF TEXAS.

    9.   THE LOAN AGREEMENT, AS AMENDED, REPRESENTS THE FINAL AGREEMENT BETWEEN
         THE PARTIES AND MAY NOT BE CONTRADICTED BY EVIDENCE OF PRIOR,
         CONTEMPORANEOUS OR SUBSEQUENT ORAL AGREEMENTS OF THE PARTIES.

         THERE ARE NO UNWRITTEN ORAL AGREEMENTS BETWEEN THE PARTIES.

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

                                     SERVICE TRANSPORT COMPANY

                                     By:  ______________________________________
                                     Name:______________________________________
                                     Title:_____________________________________

                                     ADAMS RESOURCES EXPLORATION CORPORATION

                                     By:________________________________________
                                     Name:______________________________________
                                     Title:_____________________________________

                                     BUCKLEY MINING CORPORATION

                                     By:________________________________________
                                     Name:______________________________________
                                     Title:_____________________________________

                                     CJC LEASING, INC.

                                     By:________________________________________
                                     Name:______________________________________
                                     Title:_____________________________________

                                      IV-7
<PAGE>

                                     CLASSIC COAL CORPORATION

                                     By:________________________________________
                                     Name:______________________________________
                                     Title:_____________________________________

                                     ADA MINING CORPORATION

                                     By:________________________________________
                                     Name:______________________________________
                                     Title:_____________________________________

                                     ADA RESOURCES, INC.

                                     By:________________________________________
                                     Name:______________________________________
                                     Title:_____________________________________

                                     BAYOU CITY PIPELINES, INC.

                                     By:________________________________________
                                     Name:______________________________________
                                     Title:_____________________________________

                                     BANK OF AMERICA, N.A.

                                     By:________________________________________
                                     Name:______________________________________
                                     Title:_____________________________________

                                      IV-8
<PAGE>

         Guarantor joins in the execution of this Eleventh Amendment to evidence
that it hereby agrees and consents to all of the matters contained in this
Eleventh Amendment and further agrees that (i) its liability under that certain
Guaranty Agreement dated October 27, 1993, executed by Guarantor for the benefit
of the Lender, as the same may be amended or modified from time to time (the
"Guaranty") shall not be reduced, altered, limited, lessened or in any way
affected by the execution and delivery of this Eleventh Amendment or any of the
instruments or documents referred to herein by the parties hereto, except as
specifically set forth herein or therein, (ii) the Guaranty is hereby renewed,
extended, ratified, confirmed and carried forward in all respects, (iii) the
Guaranty is and shall remain in full force and effect and is and shall remain
enforceable against Guarantor in accordance with its terms and (iv) the Guaranty
shall cover all indebtedness of the Borrowers to the Lender described in the
Loan Agreement as amended hereby.

                                     ADAMS RESOURCES & ENERGY, INC.

                                     By:________________________________________
                                     Name:______________________________________
                                     Title:_____________________________________

                                      IV-9