Document:

<PAGE>   1
                                                                   EXHIBIT 10.11

                                    AMENDMENT
                                       TO
                     AMENDMENT NO. 1 AND CONSENT AND WAIVER

         This Amendment dated March 15, 1999 to Amendment No. 1 dated as of
February 12, 1999 ("First Amendment") amends the Credit Agreement dated as of
June 12, 1998 (the "Credit Agreement") among Arkansas Best Corporation, a
Delaware corporation (the "Borrower"), the Banks party thereto, Societe
Generale, Southwest Agency, as Administrative Agent (the "Agent"), and Bank of
America National Trust and Savings Association and Wells Fargo Bank (Texas),
N.A., as Co-Documentation Agents. Capitalized terms defined in the Credit
Agreement and not otherwise defined or redefined herein are used herein with the
meanings so defined.

         WHEREAS, the Borrower requested that the Credit Agreement be amended
pursuant to Amendment No. 1 and such Amendment was approved by Majority Banks on
February 12, 1999; and

         WHEREAS, the Borrower requested that the Banks enter into this
Amendment to the First Amendment to modify certain conditions to the
effectiveness of the First Amendment and the Consent and Waiver contained
therein; and

         WHEREAS, since the date of the First Amendment the Borrower has elected
to purchase all of the existing and outstanding capital stock of Treadco, Inc.
("Treadco") not owned by the Borrower as opposed to Treadco purchasing a portion
of such capital stock; and

         WHEREAS, the Banks have agreed to so amend the First Amendment on the
terms and conditions set forth herein.

         NOW, THEREFORE, in consideration of the foregoing and for other good
and valuable consideration, the receipt and sufficiency of which are hereby
acknowledged, the parties hereto hereby agree as follows:

         Section 1. Amendment to First Amendment. The First Amendment is hereby
amended as follows:

         (a) Section 1(e) of the First Amendment is deleted in its entirety.

         (b) Section 2 of the First Amendment is deleted in its entirety.

         (c) Section 5 (c) and (d) of the First Amendment are deleted in their
             entirety.

         Section 2. Effectiveness of Amendment. This Amendment shall become
effective on the date the Agent has received counterparts of this Amendment
executed by the Borrower and the Majority Banks.

<PAGE>   2

         Section 3. Effect on Loan Documents.

         (a) Except as amended herein, the Credit Agreement and the Credit
Documents remain in full force and effect as originally executed. Nothing herein
shall act as a waiver of any of the Agent's or any of the Bank's rights under
the Credit Documents, as amended, including the waiver of any Default or Event
of Default, however denominated.

         (b) This Amendment is a Credit Document for the purposes of the
provisions of the other Credit Documents. Without limiting the foregoing, any
breach of representations, warranties, and covenants under this Amendment may be
a Default or Event of Default under other Credit Documents.

         Section 4. Fees and Expenses. The Borrower shall reimburse the Agent
for all expenses of the Agent, including charges and disbursements of legal
counsel for the Agent, in connection with the creation, amendment, modification,
waiver, or interpretation of this Amendment, and the preservation or enforcement
of any rights of the Agent or any of the Banks under this Amendment.

         Section 5. Counterparts. This Amendment may be executed in any number
of counterparts which together shall constitute an instrument.

         Section 6. Governing Law. This Amendment shall be governed by, and
construed and enforced in accordance with, the laws of the State of Texas.

         PURSUANT TO SECTION 26.02 OF THE TEXAS BUSINESS AND COMMERCE CODE, A
CREDIT AGREEMENT IN WHICH THE AMOUNT INVOLVED IN THE CREDIT AGREEMENT EXCEEDS
$50,000 IN VALUE IS NOT ENFORCEABLE UNLESS THE CREDIT AGREEMENT IS IN WRITING
AND SIGNED BY THE PARTY TO BE BOUND OR THAT PARTY'S AUTHORIZED REPRESENTATIVE.

         THE RIGHTS AND OBLIGATIONS OF THE PARTIES TO AN AGREEMENT SUBJECT TO
THE PRECEDING PARAGRAPH SHALL BE DETERMINED SOLELY FROM THE WRITTEN CREDIT
AGREEMENT, AND ANY PRIOR ORAL AGREEMENTS BETWEEN THE PARTIES ARE SUPERSEDED BY
AND MERGED INTO THE CREDIT AGREEMENT. THIS WRITTEN AMENDMENT AND THE LOAN
DOCUMENTS, AS DEFINED IN THIS AMENDMENT, REPRESENT THE FINAL AGREEMENT AMONG 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.

                     [REMAINDER OF PAGE INTENTIONALLY BLANK]

                                      -2-
<PAGE>   3

         IN WITNESS WHEREOF, the parties hereto have caused this Amendment to be
executed by their respective officers duly authorized as of the date first
written above.

                                   BORROWER:

                                   ARKANSAS BEST CORPORATION

                                   By:
                                      ------------------------------------------
                                       David E. Loeffler
                                       Vice President - Chief Financial Officer

                                   BANK:

                                   SOCIETE GENERALE,
                                       SOUTHWEST AGENCY

                                   By:
                                      ------------------------------------------
                                       Christopher Speltz
                                       Director, Head of SG - Dallas

                                   By:
                                      ------------------------------------------
                                       David C. Oldani
                                       Associate

                                      -3-
<PAGE>   4

                                   CO-DOCUMENTATION AGENTS:

                                   BANK OF AMERICA NATIONAL TRUST AND
                                            SAVINGS ASSOCIATION

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

                                      -4-
<PAGE>   5

                                   WELLS FARGO BANK (TEXAS), N.A.

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

                                      -5-
<PAGE>   6

                                   BANKS:

                                   SOCIETE GENERALE,
                                            SOUTHWEST AGENCY

                                   ---------------------------------------------
                                   Christopher J. Speltz
                                   Director - Head of SG-Dallas

                                   ---------------------------------------------
                                   David C. Oldani
                                   Associate

                                      -6-
<PAGE>   7

                                   BANK OF AMERICA NATIONAL TRUST AND
                                            SAVINGS ASSOCIATION

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

                                      -7-
<PAGE>   8

                                   WELLS FARGO BANK (TEXAS), N.A.

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

                                      -8-
<PAGE>   9

                                   ABN AMRO BANK N.V.

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

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

                                      -9-
<PAGE>   10

                                   CREDIT LYONNAIS NEW YORK BRANCH

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

                                      -10-
<PAGE>   11

                                   DEPOSIT GUARANTY NATIONAL BANK

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

                                      -11-
<PAGE>   12

                                   THE FIRST NATIONAL BANK OF CHICAGO

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

                                      -12-
<PAGE>   13

                                   NATEXIS BANQUE  BFCE

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

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

                                      -13-<PAGE>   1
                                                                   EXHIBIT 10.12

                                 AMENDMENT NO. 2

         This Amendment No. 2 dated as of August 2, 2000 ("Amendment") amends
the Credit Agreement dated as of June 12, 1998 among Arkansas Best Corporation,
a Delaware corporation (the "Borrower"), the Banks party thereto, Wells Fargo
Bank (Texas), N.A., as Administrative Agent (the "Agent"), and Bank of America
National Trust and Savings Association and Wells Fargo Bank (Texas), N.A., as
Co-Documentation Agents, as amended by Amendment No. 1 and Consent and Waiver
dated as of February 12, 1999 and Amendment to Amendment No. 1 and Consent and
Waiver dated as of March 15, 1999 (as amended, the "Credit Agreement").
Capitalized terms defined in the Credit Agreement and not otherwise defined or
redefined herein are used herein with the meanings so defined.

         WHEREAS, Wells Fargo Bank (Texas), N.A. has been appointed the
successor Administrative Agent under the Credit Agreement;

         WHEREAS, the Agent has requested that the Credit Agreement be amended
to delete references to SG and replace them with references Wells Fargo Bank
(Texas), N.A.; and

         WHEREAS, the Borrower and the Banks have agreed to so amend the Credit
Agreement on the terms and conditions set forth herein.

         NOW, THEREFORE, in consideration of the foregoing and for other good
and valuable consideration, the receipt and sufficiency of which are hereby
acknowledged, the parties hereto hereby agree as follows:

         Section 1. Amendment of Credit Agreement. The Credit Agreement is
hereby amended as follows:

         (a) Section 1.1.

             (i)  Section 1.1 is amended by adding the following new definition
         in appropriate alphabetical order:

                  "Wells" means Wells Fargo Bank (Texas), N.A..

             (ii) Section 1.1 is amended by amending the following
         definitions in their entirety:

                  "Existing Credit Agreement" means the Amended and Restated
             Credit Agreement dated as of February 21, 1996, as amended, among
             the Borrower, the banks party thereto, Societe Generale, Southwest
             Agency, as Managing Agent and Administrative Agent, and NationsBank
             of Texas, N.A., as Documentation Agent.

<PAGE>   2

                  "Prime Rate" means a fluctuating interest rate per annum as
             shall be in effect from time to time equal to the rate of interest
             publicly announced by Wells Fargo Bank (Texas), N.A. as its prime
             commercial lending rate (which may not be the lowest rate offered
             to its customers), whether or not the Borrower has notice thereof.

         (b) Section 9.2. The address for the Agent is hereby amended in its
entirety as follows:

             1445 Ross Avenue, 3rd Floor, Dallas, Texas 75201, Attention: Connor
             Duffey, Vice President (telecopy: (214) 740-1543; telephone: (214)
             740-1537)

         (c) Credit Agreement and each other Credit Document. Each reference to
"SG" in the Credit Agreement shall be amended to refer to "Wells". Each
reference to "Societe Generale, Southwest Agency" in any other Credit Document
shall be amended to refer to "Wells Fargo Bank (Texas), N.A."

         Section 2. Effectiveness of Amendment. This Amendment shall become
effective when the Agent shall have received counterparts of this Amendment
executed by the Borrower and the Majority Banks.

         Section 3. Effect on Loan Documents. Except as amended herein, the
Credit Agreement and the Credit Documents remain in full force and effect as
originally executed. Nothing herein shall act as a waiver of any of the Agent's
or any of the Bank's rights under the Credit Documents, as amended, including
the waiver of any Default or Event of Default, however denominated. This
Amendment is a Credit Document for the purposes of the provisions of the other
Credit Documents.

         Section 4. Counterparts. This Amendment may be executed in any number
of counterparts which together shall constitute an instrument.

         Section 5. Governing Law. This Amendment shall be governed by, and
construed and enforced in accordance with, the laws of the State of Texas.

         PURSUANT TO SECTION 26.02 OF THE TEXAS BUSINESS AND COMMERCE CODE, A
CREDIT AGREEMENT IN WHICH THE AMOUNT INVOLVED IN THE CREDIT AGREEMENT EXCEEDS
$50,000 IN VALUE IS NOT ENFORCEABLE UNLESS THE CREDIT AGREEMENT IS IN WRITING
AND SIGNED BY THE PARTY TO BE BOUND OR THAT PARTY'S AUTHORIZED REPRESENTATIVE.

         THE RIGHTS AND OBLIGATIONS OF THE PARTIES TO AN AGREEMENT SUBJECT TO
THE PRECEDING PARAGRAPH SHALL BE DETERMINED SOLELY FROM THE WRITTEN CREDIT
AGREEMENT, AND ANY PRIOR ORAL AGREEMENTS BETWEEN THE PARTIES ARE SUPERSEDED BY
AND MERGED INTO THE CREDIT AGREEMENT. THIS WRITTEN AMENDMENT AND THE

                                      -2-

<PAGE>   3

CREDIT DOCUMENTS, AS DEFINED IN THIS AMENDMENT, REPRESENT THE FINAL AGREEMENT
AMONG 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.

                  [Remainder of page left intentionally blank]

                                      -3-
<PAGE>   4

         IN WITNESS WHEREOF, the parties hereto have caused this Amendment to be
executed by their respective officers duly authorized as of the date first
written above.

                                 BORROWER:

                                 ARKANSAS BEST CORPORATION

                                 By:
                                    --------------------------------------------
                                      David E. Loeffler
                                      Vice President - Chief Financial Officer

                                 ADMINISTRATIVE AGENT:

                                 WELLS FARGO BANK (TEXAS), N.A.

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

                                 CO-DOCUMENTATION AGENTS:

                                 BANK OF AMERICA NATIONAL TRUST AND
                                        SAVINGS ASSOCIATION

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

                                 WELLS FARGO BANK (TEXAS), N.A.

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

                                      -4-
<PAGE>   5

                                 BANKS:

                                 WELLS FARGO BANK (TEXAS), N.A.

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

                                 BANK OF AMERICA NATIONAL TRUST AND
                                       SAVINGS ASSOCIATION

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

                                 SOCIETE GENERALE

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

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

                                 AMSOUTH BANK

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

                                      -5-
<PAGE>   6

                                 BANK ONE, NA

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

                                 ABN AMRO BANK N.V.

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

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

                                 CREDIT LYONNAIS NEW YORK BRANCH

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

                                 SUNTRUST BANK

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

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