<PAGE>   1
                                                                   EXHIBIT 10.81


                      SECOND AMENDMENT TO CREDIT AGREEMENT



         THIS SECOND AMENDMENT TO CREDIT AGREEMENT (the "Second Amendment") is
entered into effective as of August 27, 1999, by and among CRESCENT OPERATING,
INC., a Delaware corporation ("Borrower") and BANK OF AMERICA, N.A., formerly
NationsBank, N.A. (successor in interest by merger to NationsBank of Texas,
N.A.), a national banking association ("Lender"), with the acknowledgment,
confirmation, approval and agreement of the undersigned "Support Parties"
(herein so called) as set forth hereinbelow. Such Support Parties are signing
this Second Amendment solely for the purposes set forth in Section 11 of this
Second Amendment.

                              W I T N E S S E T H:

         WHEREAS, Borrower and Lender are parties to that certain Credit
Agreement dated as of August 27, 1997 (the "Original Credit Agreement") as
amended by that certain First Amendment to Credit Agreement dated effective as
of August 27, 1998 (the "First Amendment") (the Original Credit Agreement as
amended by the First Amendment is referred to in this Second Amendment as the
"Credit Agreement") and Borrower, Lender and Support Parties are parties to that
certain Support Agreement of even date with the Original Credit Agreement, as
amended and confirmed as set forth in the First Amendment (the "Support
Agreement");

         WHEREAS, Borrower and Support Parties have requested that Lender agree
to a renewal of the credit facility evidenced by the Credit Agreement and
extension of the "Termination Date" as currently defined in the Credit Agreement
and other matters as set forth herein, and Bank is willing to do so upon the
terms and conditions set forth herein; and

         WHEREAS, Borrower and Lender desire to amend the Credit Agreement by
this Second Amendment, with the acknowledgment, confirmation, approval and
agreement of the Support Parties with respect to the Support Agreement, all as
set forth hereinbelow, and the parties desire to enter into the agreements,
modifications and amendments as set forth below;

         NOW, THEREFORE, for and in consideration of the above premises and for
other good and valuable consideration, the parties hereto agree as follows:


         1. Definitions. All capitalized terms defined in the Credit Agreement,
as amended hereby, and not otherwise defined in this Second Amendment shall have
the same meanings as assigned to them in the Credit Agreement when used in this
Second Amendment, unless the context hereof shall otherwise require or provide.


         2. Representations and Warranties. In order to induce Lender to enter
into this Second Amendment, Borrower represents and warrants to Lender that:

                  A. This Second Amendment, the Credit Agreement, as amended
hereby, and the Loan Papers are the legal and binding obligations of Borrower,
enforceable in accordance with their respective terms, except as limited by
bankruptcy, insolvency or other laws of general application relating to the
enforcement of creditors' rights;

                  B. No event has occurred and is continuing which constitutes a
Default or a Potential Default; and

                  C. All of the representations and warranties contained in
Paragraph 5 of the Credit Agreement, as amended by this Second Amendment, are
true and correct as of the date hereof.




                                  Page 1 of 5
<PAGE>   2

         3. Amendments to Credit Agreement.

                  A. In order to renew and extend the credit facility evidenced
by the Credit Agreement, as amended by this Second Amendment, and the Loan
Papers, the definition of the term "Termination Date" as set forth in the Credit
Agreement is hereby amended and restated in its entirety to read as follows:

                  Termination Date means the earlier to occur of the following
         dates: (a) August 31, 2001; and (b) the effective date that Lender's
         commitment to extend credit under this agreement is otherwise canceled
         or terminated in accordance with this agreement.

                  B. Paragraph 5 of the Credit Agreement is hereby amended to
replace clause (k) thereof with the following clause (k):

                  (k) use its best efforts to complete offerings(s) and/ or
                  private placement(s) of securities of Borrower comprising a
                  Successful Rights Offering prior to August 31, 2001; provided
                  that Borrower will utilize the Support Agreement dated August
                  27, 1997, executed by Richard E. Rainwater, John Goff and
                  Gerald Haddock in connection herewith, as it may be modified,
                  amended, confirmed or restated, if necessary in order to
                  accomplish the foregoing and pay the Obligation in full when
                  due, and Borrower specifically agrees to take all reasonable
                  and necessary action to enforce such Support Agreement in such
                  instance and/or, at the request of Lender, to join Lender in
                  any such enforcement action;

                  C. Without affecting in any way the obligations of Richard E.
Rainwater and John Goff as "Support Parties" under the Support Agreement
(including without limitation as referred to in Paragraph 5 of the Credit
Agreement), Gerald Haddock is hereby released from his obligations as a "Support
Party" under such Support Agreement, and the name "Gerald Haddock" is hereby
deleted from Paragraph 7 of the Credit Agreement and Paragraph 9 of the Credit
Agreement.

                  D. The promissory note in the face principal amount of
$15,000,000.00 dated August 27, 1997 executed by Borrower and payable to Lender
(or its predecessors in interest) and executed in connection with the Original
Credit Agreement is hereby renewed and extended to be evidenced by that certain
promissory note dated of even date herewith in the face principal amount of
$15,000,000.00 executed by Borrower and payable to Lender (sometimes referred to
in this Second Amendment and in connection herewith as the "Renewal Note"),
which the parties agree and acknowledge to be the "Note" as contemplated in
Paragraph 4(a) of the Credit Agreement and a "Loan Paper" as defined in the
Credit Agreement.

                  E. The definition of the term "Lender" as set forth in the
Credit Agreement and all references to "Lender" in the Credit Agreement and in
the other Loan Papers are hereby amended to refer to Bank of America, N.A.,
formerly NationsBank, N.A. (successor in interest by merger to NationsBank of
Texas, N.A.).

         4. Conditions Precedent. This Second Amendment and the obligations of
Lender hereunder are subject to the conditions precedent that Lender shall have
received from Borrower, together with this Second Amendment duly executed by
Borrower, Richard E. Rainwater and John Goff: (i) the Renewal Note, duly
executed by Borrower, and any other documents requested by Lender prior to
closing in connection herewith, all in form and substance satisfactory to
Lender, (ii) payment of Lender's costs and expenses incurred in connection
herewith as contemplated in the Credit Agreement including, without limitation,
the reasonable attorney's fees of the Lender's legal counsel and any other
costs, expenses and disbursements incurred by Lender through the date of
execution of this Second Amendment, and (iii) payment of a non-refundable
facility fee (the "Facility Fee") in the amount of $75,000.00. The parties each
acknowledge and agree that the Facility Fee payable hereunder is a bona fide fee
intended as reasonable compensation to Lender for committing to make funds
available to Company as described in the Credit





                                  Page 2 of 5
<PAGE>   3
Agreement, as amended by this Second Amendment, and the administration of such
credit facility and for no other purpose.

         5. Further Assurances. Borrower shall make, execute or endorse, and
acknowledge and deliver or file or cause same to be done, all such documents,
notices or other assurances, and take all such other action, as Lender may, from
time to time, deem reasonably necessary or proper in connection with this Second
Amendment and the Credit Agreement, as amended hereby.

         6. Scope of Amendments. Any and all other provisions of the Credit
Agreement and any other Loan Papers are hereby amended and modified wherever
necessary and even though not specifically addressed herein, so as to conform to
the amendments and modifications set forth in this Second Amendment.

         7. Limitation on Agreements. The amendments set forth herein are
limited in scope as described herein and shall not be deemed (a) to be a consent
under or waiver of any other term or condition of the Credit Agreement or any of
the Loan Papers, or (b) to prejudice any right or rights which Lender now has or
may have in the future under, or in connection with the Credit Agreement as
amended by this Second Amendment, the Note, the Loan Papers or any of the
documents referred to herein or therein.

         8. Governing Law. This Second Amendment has been prepared, in being
executed and delivered and is intended to be performed in the State of Texas,
and the substantive laws of such state and the applicable federal laws of the
United States of America shall govern the validity, construction, enforcement
and interpretation of this Second Amendment.

         9. ARBITRATION. ANY CONTROVERSY OR CLAIM BETWEEN OR AMONG THE PARTIES
HERETO, INCLUDING, BUT NOT LIMITED TO, THOSE ARISING OUT OF OR RELATING TO THIS
AGREEMENT OR ANY RELATED AGREEMENTS OR INSTRUMENTS, INCLUDING ANY CLAIM BASED ON
OR ARISING FROM AN ALLEGED TORT, SHALL BE DETERMINED BY BINDING ARBITRATION IN
ACCORDANCE WITH THE FEDERAL ARBITRATION ACT (OR IF NOT APPLICABLE, THE
APPLICABLE STATE LAW). THE RULES OF PRACTICE AND PROCEDURE FOR THE ARBITRATION
OF COMMERCIAL DISPUTES OF JUDICIAL ARBITRATION AND MEDIATION SERVICES, INC.
(J.A.M.S.), AND THE "SPECIAL RULES" SET FORTH BELOW. IN THE EVENT OF ANY
INCONSISTENCY, THE SPECIAL RULES SHALL CONTROL. JUDGMENT UPON ANY ARBITRATION
AWARD MAY BE ENTERED IN ANY COURT HAVING JURISDICTION. ANY PARTY TO THIS CREDIT
AGREEMENT MAY BRING AN ACTION, INCLUDING A SUMMARY OR EXPEDITED PROCEEDING, TO
COMPEL ARBITRATION OF ANY CONTROVERSY OR CLAIM TO WHICH THIS AGREEMENT APPLIES
IN ANY COURT HAVING JURISDICTION OVER SUCH ACTION.

         A. SPECIAL RULES. THE ARBITRATION SHALL BE CONDUCTED IN THE CITY OF THE
BORROWER'S DOMICILE AT TIME OF THIS AGREEMENT'S EXECUTION AND ADMINISTERED BY
J.A.M.S. WHO WILL APPOINT AN ARBITRATOR; IF J.A.M.S. IS UNABLE OR LEGALLY
PRECLUDED FROM ADMINISTERING THE ARBITRATION, THEN THE AMERICAN ARBITRATION
ASSOCIATION WILL SERVE. ALL ARBITRATION HEARINGS WILL BE COMMENCED WITHIN NINETY
(90) DAYS OF THE DEMAND FOR ARBITRATION; FURTHER, THE ARBITRATOR SHALL ONLY,
UPON A SHOWING OF CAUSE, BE PERMITTED TO EXTEND THE COMMENCEMENT OF SUCH HEARING
FOR UP TO AN ADDITIONAL SIXTY (60) DAYS.

         B. RESERVATION OF RIGHTS. NOTHING IN THIS AGREEMENT SHALL BE DEEMED TO:
(I) LIMIT THE APPLICABILITY OF ANY OTHERWISE APPLICABLE STATUTES OF LIMITATION
OR REPOSE AND ANY WAIVERS CONTAINED IN THIS AGREEMENT; OR (II) BE A WAIVER BY
THE LENDER OF THE PROTECTION AFFORDED TO IT BY 12 U.S.C. SEC. 91 OR ANY
SUBSTANTIALLY EQUIVALENT STATE LAW; OR (III) LIMIT THE RIGHT OF THE LENDER
HERETO: (A) TO EXERCISE SELF HELP REMEDIES SUCH AS (BUT NOT LIMITED TO) SETOFF,
OR (B) TO FORECLOSE AGAINST ANY REAL OR PERSONAL PROPERTY COLLATERAL, OR (C) TO
OBTAIN FROM A COURT PROVISIONAL OR ANCILLARY REMEDIES SUCH AS (BUT NOT LIMITED
TO) INJUNCTIVE RELIEF, WRIT OF POSSESSION OR THE APPOINTMENT OF A RECEIVER. THE
LENDER MAY EXERCISE SUCH SELF HELP RIGHTS, FORECLOSE UPON SUCH PROPERTY, OR
OBTAIN SUCH PROVISIONAL OR ANCILLARY REMEDIES BEFORE, DURING OR AFTER THE
PENDENCY OF ANY ARBITRATION PROCEEDING BROUGHT PURSUANT TO THIS AGREEMENT.
NEITHER THIS EXERCISE OF SELF HELP REMEDIES NOR THE INSTITUTION OR MAINTENANCE
OF AN ACTION FOR FORECLOSURE OR PROVISIONAL OR ANCILLARY REMEDIES SHALL
CONSTITUTE A WAIVER OF THE RIGHT OF ANY PARTY, INCLUDING THE CLAIMANT IN ANY
SUCH ACTION, TO ARBITRATE THE MERITS OF THE CONTROVERSY OR CLAIM OCCASIONING
RESORT TO SUCH REMEDIES.



                                  Page 3 of 5
<PAGE>   4

         10. Multiple Counterparts. This Second Amendment may be executed in any
number of counterparts, all of which taken together shall constitute one and the
same agreement, and any of the parties hereto may execute this Second Amendment
by signing any such counterpart.

         11. Signatures of Support Parties. By signing below where indicated,
the undersigned Support Parties each (a) acknowledge this Second Amendment and
the Credit Agreement as amended hereby; (b) agree with the terms, conditions and
amendments contained in this Second Amendment and the Credit Agreement as
amended hereby as they relate to the Support Agreement, including without
limitation, the amended definition of "Termination Date" as set forth in this
Second Amendment; (c) agree that the Support Agreement shall be amended as
follows: (i) Gerald Haddock is hereby released from his obligations as a
"Support Party" as contemplated therein, (ii) the term "Target Date" as used in
the Support Agreement shall be amended to be August 31, 2001, (iii) the word
"renewed," shall be inserted after the comma between the words "increased" and
"extended" contained on the first line of clause c of Section 1 of the Support
Agreement, (iv) the name of the "Bank" shall be changed to "Bank of America,
N.A., formerly NationsBank, N.A. (successor in interest by merger to NationsBank
of Texas, N.A.)" and (v) the Support Agreement shall be deemed to be further
amended wherever necessary in order to continue the obligations of the
undersigned Support Parties contained in the Support Agreement and conform to
the changes reflected in this Second Amendment; and (d) confirm their continuing
obligations under the Support Agreement, as amended hereby, which shall continue
in full force and effect as contemplated therein and herein, until the
Obligation has been paid in full and Lender shall have no further commitment to
make Advances.

THE CREDIT AGREEMENT AND THE SUPPORT AGREEMENT, AS EACH IS AMENDED BY THIS
SECOND AMENDMENT, AND THE OTHER LOAN PAPERS REPRESENT 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 hereto have caused this Second
Amendment to be executed to be effective as of the date and year first above
written.


                               LENDER:

                               BANK OF AMERICA, N.A., formerly NationsBank, N.A.


                               By:
                                   -------------------------------------------
                                   Cary C. Conwell, Senior Vice President


                               BORROWER:

                               CRESCENT OPERATING, INC., a Delaware corporation


                               By:
                                    ------------------------------------------
                                    Jeff Stevens, Executive Vice President
                                         and Chief Operating Officer









                                  Page 4 of 5
<PAGE>   5

THE CREDIT AGREEMENT AND THE SUPPORT AGREEMENT, AS EACH IS AMENDED BY THIS
SECOND AMENDMENT, AND THE OTHER LOAN PAPERS REPRESENT 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.

                                        SUPPORT PARTIES:


                                        ---------------------------------------
                                        RICHARD E. RAINWATER

                                        ---------------------------------------
                                        JOHN GOFF



                                  Page 5 of 5