<PAGE>

                                   EXHIBIT 10

                                 LOAN AGREEMENT

         THIS LOAN AGREEMENT (hereinafter called "this Agreement") is made and
entered into this 15th day of September, 2001, by and between SUMMIT BANCSHARES,
INC., a Texas corporation, having its principal place of business at 1300
Summit, Suite 604, Fort Worth, Texas 76102 (hereinafter called "Borrower"), and
THE FROST NATIONAL BANK, a national banking association, with its main banking
offices located at 100 West Houston Street, P.O. Box 1600, San Antonio, Texas
78296 (hereinafter called "Lender").

         WHEREAS, Borrower is desirous of obtaining from Lender two loans
represented by two promissory notes in the aggregate principal amount of
$11,000,000.00 for the purpose of providing short term liquidity to the Borrower
and to finance bank acquisitions; and

         WHEREAS, Lender is desirous of making such loans to Borrower in the
aggregate principal amount of $11,000,000.00 for the purposes set forth above,
but on the terms, conditions and covenants hereafter contained;

         NOW, THEREFORE, subject to all terms, conditions and covenants
hereinafter set forth and in consideration of the premises and the mutual
covenants contained herein, the parties hereto agree as follows:

                                    ARTICLE I

                                   Definitions
                                   -----------

         The terms defined in this Article I (except as otherwise expressly
provided in this Agreement) for all purposes shall have the following meanings:

         "Acquisition Note" shall mean the promissory note so referenced in
          ----------------
Section 2.01 of this Agreement.

         "Advance" shall mean the amounts requested by Borrower from time to
          ----------------
time as set forth in Section 2.01 of this Agreement.

         "Advance Request Form" means a document in the form of attached Exhibit
          ----------------
"A", properly completed and signed by Borrower requesting an Advance.

         "Average Assets" shall mean the average of the assets most recently
          ----------------
reported by a bank to its regulatory authorities calculated in accordance with
regulatory accounting principles consistently applied.

<PAGE>

         "Bad Debt Ratio" shall mean the ratio of the reserve for bad debts to
          --------------
total loans.

         "Bank" shall mean, collectively, Summit Bank, N.A., Fort Worth, Texas,
          ----
whose principal place of business is 1300 Summit, Fort Worth, Texas 76102 and
all other banks and financial institutions, whether chartered by the federal
government or any State, which are acquired after Closing Date by Borrower or
its Subsidiaries with proceeds of the Loan evidenced by the Acquisition Note.

         "Book Value" shall mean, for any share of Bank stock, Bank's Equity
          ----------
Capital divided by the total number of Bank shares outstanding.

         "Business Day" shall mean a day on which Lender is open for transaction
          ------------
of its general banking business.

         "Capital Ratio" shall mean the ratio of Bank's Equity Capital to Bank's
          -------------
assets as determined by regulatory accounting principles consistently applied.

         "Cash Flow Coverage" shall mean the ratio of (i) the Borrower's
          ------------------
consolidated Net Income plus non-cash charges plus depreciation plus
amortization plus loan loss provisions to (ii) the current maturities of long
term debt, all as determined in accordance with GAAP.

         "Classified Assets" means, at any particular time, all assets of Bank
          -----------------
classified, in whole or in part, as "Loss," "Doubtful," "Substandard," or "Other
Assets Especially Mentioned" by Bank or any governmental or regulatory
authority.

         "Closing Date" shall mean the date this Agreement is executed by all
          ------------
parties hereto which shall be the day and year first written above unless
otherwise indicated. The Closing shall take place at Borrower's offices, or at
such other place as the parties shall mutually agree.

         "Collateral" shall have the meaning ascribed to it in Section 2.03.
          ----------

         "Equity Capital" shall mean the Tier I Capital as defined by the
          --------------
Federal Reserve Regulations.

         "Event of Default" means any event specified in Section 6.01 of this
          ----------------
Agreement, provided that any requirement in connection with such event for the
giving of notice or lapse of time or any other condition has been satisfied.

         "GAAP" means generally accepted accounting principles, applied on a
          ----
consistent basis, as set forth in Opinions of the Accounting Principles Board of
the American Institute of Certified Public Accountants and/or in statements of
the Financial Accounting Standards Board and/or their respective successors and
which are applicable in the circumstances as of the date in question. Accounting
principles are applied on a "consistent basis" when the accounting principles
observed

<PAGE>

in a current period are comparable in all material respects to those accounting
principles applied in a preceding period.

         "Insider" shall mean an "executive officer," "director," or "person who
          -------
directly or indirectly or in concert with one or more persons, owns, controls,
or has the power to vote more than 10% of any class of voting securities" (as
such terms are defined in the Financial Institutions Regulatory and Interest
Rate Control Act of 1978, as amended, or in regulations promulgated pursuant
thereto) of Borrower or any Subsidiary.

         "Highest Lawful Rate" shall mean the maximum rate of nonusurious
          -------------------
interest allowed from time to time by Law. In no event shall Chapter 346 of the
Texas Finance Code (which regulates certain revolving loan accounts and
revolving tri-party accounts) apply to this Loan. To the extent that Chapter 303
of the Texas Finance Code is applicable to this Loan, the "weekly ceiling"
specified in such article is the applicable ceiling; provided that, if any
applicable law permits greater interest, the law permitting the greatest
interest shall apply.

         "Laws" shall mean all statutes, laws, ordinances, regulations, orders,
          ----
writs, injunctions, or decrees of the United States, any state or commonwealth,
any municipality, or any Tribunal.

         "LIBOR" shall mean the London Interbank Offered Rate (LIBOR) for three
          -----
months quoted on the first business day of each calendar quarter in The Wall
                                                                    --------
Street Journal (Southwest Edition) in the "Money Rates" column. If the Wall
--------------
Street Journal London Interbank Offered Rate ceases to be made available by the
publisher, or any successor to the publisher of The Wall Street Journal,
                                                -----------------------
(Southwest Edition), the interest rate will be determined by using a comparable
index. If more than one Wall Street Journal London Interbank Offered Rate for
three months is quoted, the higher rate shall apply. The Wall Street Journal
London Interbank Offered Rate is a reference rate and does not necessarily
represent the lowest or best rate actually charged to any customer.

         "Liquidity Note" shall mean the promissory note so referenced in
          --------------
Section 2.01 of this Agreement.

         "Loans" shall mean extensions of credit to Borrower pursuant to Section
          -----
2.01 of this Agreement.

         "Loan Documents" shall mean this Agreement, the Acquisition Note,
          --------------
Liquidity Note, the Security Instruments, and all instruments or documents
executed and delivered pursuant to or in connection with this Agreement and any
future amendments hereto or thereto, and all renewals and extensions thereof.

         "Net Income" shall mean that amount of income remaining after deducting
          ----------
expenses (including provision for loan and lease losses) and payments of all
taxes incurred on said income and after deducting securities transactions, all
as calculated in accordance with GAAP and regulatory accounting principles, to
the extent each is applicable.

<PAGE>

         "Non-Performing Loans" means loans on nonaccrual, loans on which the
          --------------------
interest rate has been reduced other than to reflect the then prevailing market
interest rates, loans which have been past due for ninety (90) days or more, and
Other Real Estate.

         "Non-Performing Loans Ratio" means the ratio of the reserve for bad
          --------------------------
debts to Non-Performing Loans.

         "Notes" shall mean the promissory notes evidencing the Loans executed
          -----
pursuant to Section 2.02 of this Agreement and any promissory note issued in
substitution therefor or in renewal or extension or rearrangement thereof.

         "Obligations" shall mean the outstanding principal amounts of the Notes
          -----------
and interest accrued thereon, and any and all other indebtedness, liabilities
and obligations whatsoever of Borrower to Lender hereunder or under the Notes
and/or the Security Instruments and all renewals, modifications and extensions
thereof, plus interest accruing on any foregoing and all attorney fees and costs
incurred in the enforcement of any foregoing.

         "Other Real Estate" shall mean the real property owned by Bank as a
          -----------------
result of foreclosure, deeds in lieu of foreclosure, or judicial process, or
received as partial payment of a note, specifically excluding real estate
occupied by Bank in the conduct of its ordinary course of business.

         "Person" shall mean any individual, firm, corporation, association,
          ------
partnership, joint venture, trust or other entity, or Tribunal.

         "Prime Rate" shall mean the variable rate of interest per annum
          ----------
established by The Frost National Bank from time to time and referred to as its
"prime rate". Such rate is set by Lender as a general reference rate of
interest, taking into account such factors as Lender may deem appropriate, it
being understood that many of Lender's commercial or other loans are priced in
relation to such rate, that it is not necessarily the lowest or best rate
actually charged to any customer and that Lender may make various commercial or
other loans at rates of interest having no relationship to such rate.

         "Return on Average Assets" shall mean the ratio of Net Income to the
          ------------------------
Average Assets.

         "Return on Equity Capital" shall mean the ratio of Net Income to the
          ------------------------
average Equity Capital.

         "Security Instruments" shall mean the Security Agreement-Pledge
          --------------------
referred to in Section 2.03 of this Agreement and any other documents securing
the Obligations.

<PAGE>

         "Subsidiary" means any corporation or bank of which more than fifty
          ----------
(50%) of the issued and outstanding securities having ordinary voting power for
the election of a majority of directors is owned or controlled, directly or
indirectly, by Borrower, by Borrower with one or more Subsidiaries, or by just
one or more Subsidiaries.

         "Tangible Net Worth" means, at any particular time, all amounts which,
          ------------------
in conformity with GAAP, would be included as stockholders' equity on a balance
sheet; provided, however, there is excluded therefrom: (i) any amount at which
shares of capital stock of Borrower (treasury shares) appears as an asset on the
balance sheet, (ii) goodwill, including any amounts, however designated, that
represent the excess of the purchase price paid for assets or stock over the
value assigned thereto, (iii) patents, trademarks, trade names, and copyrights,
and (iv) all other assets which are properly classified as intangible assets.

         "Taxes" shall mean all taxes, assessments, fees, or other charges from
          -----
time to time or at any time imposed by any Laws or by any Tribunal.

         "Tribunal" shall mean any state, commonwealth, federal, foreign,
          --------
territorial, regulatory, or other court or governmental department, commission,
board, bureau, agency or instrumentality.

         1.02 Other Definitional Provisions. All definitions contained in this
              -----------------------------
Agreement are equally applicable to the singular and plural forms of the terms
defined. The words "hereof," "herein," and "hereunder" and words of similar
import referring to this Agreement refer to this Agreement as a whole and not to
any particular provision of this Agreement. Unless otherwise specified, all
Article and Section references pertain to this Agreement. All accounting terms
not specifically defined herein shall be construed in accordance with GAAP.

                                   ARTICLE II

                     Loan, Security and Conditions Precedent

         2.01 The Loans. Subject to the terms and conditions of this Agreement,
              ---------
Lender agrees to make the Loans to Borrower evidenced by two promissory notes,
one note in the principal amount of $10,000,000.00 shall be for the sole purpose
of financing bank acquisitions (the "Acquisition Note") and the second note in
the principal amount of $1,000,000.00 shall be for the purpose of providing
short term liquidity to the Borrower (the "Liquidity Note").

         2.02 The Notes. The obligation of Borrower to pay the Loans shall be
              ---------
evidenced by the Acquisition Note and Liquidity Note each executed by Borrower
and payable to the order of Lender, in the principal amount of each Note bearing
interest as therein provided. Unpaid and past due principal and interest shall
bear interest at the rate of four percent (4.0%) per annum above the Prime Rate.
The Borrower shall pay principal and interest in accordance with the terms of
each Note, with the maturity date being as set forth in each Note.

<PAGE>

                  (a) Acquisition Note. From Closing Date and continuing at all
                      ----------------
         times through September 15, 2002 (the "Revolving Credit Period") the
         Loan evidenced by the Acquisition Note shall be a revolving credit
         facility which will allow the Borrower to request such amounts as
         Borrower may elect from time to time (each such amount being herein
         called an "Advance") so long as the aggregate amount of Advances
         outstanding at any time under the Acquisition Note does not exceed Ten
         Million and NO/100 Dollars ($10,000,000.00) provided however, the
         minimum Advance must be at least $500,000.00. The Borrower shall have
         the right to borrow, repay, and borrow again under the credit facility.
         Interest shall be due and payable quarterly and shall accrue at the
         election of the Borrower (which election shall be made on the date of
         the first Advance) at either LIBOR plus 200 basis points or the Prime
         Rate. The outstanding principal balance of the Acquisition Note on
         September 15, 2002 shall convert to a term facility (the "Term Period")
         and shall be payable in accordance with the terms of the Acquisition
         Note.

                  (b) Liquidity Note. The Liquidity Note shall be due and
                      --------------
         payable as follows: during the Revolving Credit Period, the Loan
         evidenced by the Liquidity Note shall be a revolving credit facility
         which will allow the Borrower to request such amounts as Borrower may
         elect from time to time (each such amount being herein called an
         "Advance") so long as the aggregate amount of Advances outstanding at
         any time under the Liquidity Note does not exceed One Million and
         NO/100 Dollars ($1,000,000.00) provided however, the minimum Advance
         must be at least $50,000.00. The Borrower shall have the right to
         borrow, repay, and borrow again under the credit facility. Interest
         shall be due and payable quarterly and shall accrue at the Prime Rate.
         The outstanding principal balance of the Liquidity Note on September
         15, 2002 shall convert to a term facility (the "Term Period") and shall
         be payable in accordance with the terms of the Liquidity Note.

                  (c) Revolving Principal Balance. It is contemplated that by
                      ---------------------------
         reason of payments or prepayments there may be times when no
         indebtedness is owing under the Loans; but notwithstanding such
         occurrences, each Note shall remain valid and shall be in full force
         and effect as to loans or Advances made pursuant to and under the terms
         of each Note subsequent to each such occurrence. All loans or Advances
         and all payments or prepayments made on account of principal or
         interest shall be endorsed by the holder of each Note on a schedule
         attached thereto and made a part thereof for all purposes. In the event
         that the unpaid principal amount at any time, for any reason, exceeds
         the maximum amount specified in each Note, Borrower covenants and
         agrees to immediately pay to the Lender the excess principal amount,
         such excess principal amount shall in all respects be deemed to be
         included among the loans or Advances made pursuant to the other terms
         of each Note and shall bear interest at the rates hereinabove stated.

                  (d) Interest Calculation. Adjustments in the interest rate
                      --------------------
         shall be made on the date as any change in LIBOR or the Prime Rate and
         adjustments due to changes in the Highest Lawful Rate to be made on
         the effective date of any change in the Highest Lawful Rate. Interest
         shall be computed on a per annum basis of a year of 360 days and for
         the

<PAGE>

         actual number of days (including the first but excluding the
         last day) elapsed unless such calculation would result in a usurious
         rate, in which case interest shall be calculated on a per annum basis
         of a year of 365 or 366 days, as the case may be. It is the intention
         of Borrower and Lender to conform strictly to applicable usury laws.
         Accordingly, if the transactions contemplated hereby would be usurious
         under applicable law, then, in that event, notwithstanding anything to
         the contrary herein or in any agreement entered into in connection with
         or as security for this Loan, it is agreed as follows: (i) the
         aggregate of all consideration which constitutes interest under
         applicable law that is taken, reserved, contracted for, charged or
         received under this Loan or under any of the other Loan Documents or
         otherwise in connection with this note shall under no circumstances
         exceed the maximum amount of nonusurious interest allowed by applicable
         law, and any excess shall be credited on this Loan by the holder hereof
         (or, to the extent that this note shall have been or would thereby be
         paid in full, then it shall be applied to any other indebtedness of
         Borrower to Lender, or to the extent all other indebtedness has been or
         would thereby be paid in full, refunded to Borrower); and (ii) in the
         event that maturity of this Loan is accelerated by reason of an
         election by the holder hereof resulting from any default hereunder or
         otherwise, or in the event of any required or permitted prepayment,
         then such consideration that constitutes interest may never include
         more than the maximum amount of nonusurious interest allowed by
         applicable law, and excess interest, if any, provided for in this note
         or otherwise shall be cancelled automatically as of the date of such
         acceleration or prepayment and, if theretofore prepaid, shall be
         credited on this Loan (or, to the extent that this Loan shall have been
         or would thereby be paid in full, then it shall be applied to any other
         indebtedness of Borrower to Lender, or to the extent all other
         indebtedness has been or would thereby be paid in full, refunded to
         Borrower).

         2.03 Security for the Loan. To secure full and complete payment and
              ---------------------
performance of the Obligations, Borrower shall execute and deliver the following
documents (which, together with all property which may hereafter be delivered to
secure the Obligations, being herein called "Collateral"):

                  (i) A Security Agreement-Pledge wherein the Borrower shall
              pledge and grant to Lender a first priority security interest in
              100% of the shares of common stock of Summit Bank, N.A. and all
              productsand proceeds thereof. Lender shall retain possession of
              the certificate(s) representing said common stock, together with
              v powers executed in blank by Borrower.

         2.04 Conditions Precedent to Closing. The obligation of Lender to make
              -------------------------------
the Loans shall be subject to the conditions precedent that Lender shall have
received on or before the day of the making of the Loan, the following
documents, in form and substance satisfactory to Lender:

              (a) Notes.  The Notes executed by Borrower.
                  -----

<PAGE>

                  (b) Security Instruments. The Security Instruments executed by
                      --------------------
          Borrower granting to Lender a security interest in the Collateral.

                  (c) Stock Certificates, Powers, UCC-1. The original stock
                      ---------------------------------
          certificates pledged as collateral, the executed stock powers and
          financing statements to evidence the security interest granted in the
          Security Instruments.

                  (d) Resolutions. Corporate resolutions of the Board of
                      -----------
         Directors of Borrower, certified by the Secretary of such corporation,
         which resolution authorize the execution, delivery and performance by
         Borrower of this Agreement and the other Loan Documents. Included in
         said resolutions or by separate document, the Lender shall receive a
         certificate of incumbency certified by the Secretary of Borrower
         certifying the names of each officer authorized to execute this
         Agreement and the other Loan Documents, together with specimen
         signatures of such officers.

                  (e) Articles of Incorporation. Copies of the Articles of
                      -------------------------
          Incorporation of Borrower and the Articles of Association of Summit
          Bank, N.A. certified to be true and correct by the Secretary of such
          corporation and cashier of such Bank, respectively.

                  (f) Bylaws. The Bylaws of Borrower and Summit Bank, N.A.
                      ------
          certified to be true and correct by the Secretary of such corporation
          and cashier of such Bank, respectively.

                  (g) Government Certificates. Certificate of Good Standing of
                      -----------------------
         Borrower (if appropriate) issued by the Comptroller of Public Accounts
         of the State of Texas; Certificate of Existence of Borrower and each
         Subsidiary (if appropriate) issued by the Secretary of State of Texas;
         certificate of good standing of Bank from the appropriate regulatory
         authority; and a copy of the Letter of Approval from the Board of
         Governors of the Federal Reserve Bank approving Borrower's application
         as a bank holding company (or such other documentation acceptable to
         Lender to evidence the Borrower's status as a bank holding company).

                  (h) Opinion of Borrower's Counsel. Lender shall have received
                      -----------------------------
         from Borrower's counsel an opinion satisfactory in form and substance
         to Lender and its counsel.

                  (i) Financial Statements. Borrower and its Subsidiaries shall
                      --------------------
         have each delivered to Lender such financial statements as shall have
         been requested by Lender, in form and substance satisfactory to Lender
         in its sole discretion.

                  (j) Additional Papers. Borrower shall have delivered to Lender
                      -----------------
         such other documents, records, instruments, papers, opinions, and
         reports, as shall have been requested by Lender, to evidence the status
         or organization or authority of Borrower or to evidence or secure
         payment of the Obligations, all in form satisfactory to Lender and its
         counsel.

<PAGE>

                                   ARTICLE III

                         Representations and Warranties
                         ------------------------------

         To induce Lender to enter into this Agreement and upon which Lender has
relied in entering into this Agreement and consummating the transactions herein
described, Borrower represents and warrants to Lender that:

         3.01  Organization of Borrower. Borrower is a corporation duly
               ------------------------
organized, validly existing, and in good standing under the laws of the State of
Texas; Borrower is duly authorized, qualified under all applicable Laws to
conduct its businesses; and Borrower has full power, capacity, authority and
legal right to conduct the businesses in which it does now, and propose to,
engage; and Borrower has full power, capacity, authority and legal right to
execute and deliver and to perform and observe the provisions of this Agreement,
and the other Loan Documents, to which it is a party, all of which have been
duly authorized and approved by all necessary corporate action. Summit Bank,
N.A. is a national banking association duly organized, validly existing and in
good standing under the laws of the United States of America.

         3.02  Litigation. No action, suit or proceeding against or affecting
               ----------
Borrower or any Subsidiary is known to be pending, or to the knowledge of
Borrower threatened, in any court or before any governmental agency or
department, which, if adversely determined, could result in a final judgment or
liability of a material amount not fully covered by insurance, or which may
result in any material adverse change in the business, or in the condition,
financial or otherwise, of Borrower. There are no outstanding judgments against
Borrower or any Subsidiary.

         3.03  Compliance With Other Instruments. There is no default in the
               ---------------------------------
performance of any material obligation, covenant, or condition contained in any
agreement to which Borrower is a party which has not been waived. Neither
Borrower nor any Subsidiary is in material default with respect to any Law of
any Tribunal. The execution, delivery and performance of the terms of this
Agreement, the Notes and the other Loan Documents by Borrower will not violate
the provisions of any Law applicable to Borrower. Borrower's By-laws or Articles
of Incorporation, or any order or regulation of any governmental authority to
which the Borrower is subject, and will not conflict with or result in a breach
of any of the terms of any agreement or instrument to which Borrower is a party
or by which Borrower is bound, or constitute a default thereunder, or result in
the creation of a lien, charge, or incumbrance of any nature upon any of
Borrower's properties or assets.

         3.04  No Default. No Event of Default specified in Article VI has
               ----------
occurred and is continuing.

         3.05  Corporate Authorization. Borrower's Board of Directors have duly
               -----------------------
authorized the execution and delivery of this Agreement and the other Loan
Documents to which it is a party and

<PAGE>

the performance of their respective terms and no consent of the stockholders of
Borrower or any other Person is a prerequisite thereto or if a prerequisite
thereto, the same has been duly obtained. This Agreement and all other Loan
Documents are valid, binding, and enforceable obligations of Borrower in
accordance with their respective terms.

         3.06  Disclosure. Neither this Agreement nor any other document,
               ----------
certificate, Loan Document or statement furnished to Lender by or on behalf of
Borrower in connection herewith is known to contain any untrue statement of a
material fact or, to the knowledge of Borrower, omits to state a material fact
necessary in order to make the statements contained herein and therein not
misleading.

         3.07  Ownership of Subsidiaries. Except as otherwise disclosed to
               -------------------------
Lender, Borrower owns 100% of the issued and outstanding capital stock of Summit
Bank, N.A. Except as otherwise disclosed to Lender, Borrower does not own,
directly or indirectly, any stock or any interest in any other Person.

         3.08  Federal Reserve Board Regulations. Borrower is not engaged
               ---------------------------------
principally, or as one of its important activities, in the business of extending
credit for the purpose of purchasing or carrying margin stock (within the
meaning of Regulation G, T, U, or X of the Board of Governors of the Federal
Reserve System) and no part of the proceeds of the Loan will be used to purchase
or carry any margin stock or to extend credit to others for the purpose of
purchasing or carrying any margin stock except as otherwise disclosed in writing
to Lender. Neither Borrower nor any agent acting on its behalf has taken or will
take any action which might cause Borrower's execution of this Agreement to
violate any regulation of the Board of Governors of the Federal Reserve System
or to violate the Securities Act of 1933 or the Securities Exchange Act of 1934,
as amended.

         3.09  Stock and Stock Agreements. Neither Borrower nor any Subsidiary
               --------------------------
has any class of stock authorized other than common stock. Further, Borrower has
furnished to Lender copies of all buy-sell agreements, stock redemption
agreements, voting trust agreements and all other agreements and contracts
involving the stock of Borrower and/or each of its Subsidiaries to which
Borrower or any Subsidiary is a party and there are not now any agreements or
terms of any agreements to which Borrower or any Subsidiary is a party which
alter, impair, affect or abrogate the rights of Lender or the Obligations of
Borrower under this Agreement or any other Loan Document.

         3.10  Financial Statements. The consolidated financial statements of
               --------------------
Borrower, dated as of December 31, 2000, and furnished to Lender, were prepared
in accordance with regulatory accounting principles or GAAP, as indicated upon
such statements, and such statements fairly present, as appropriate, the
consolidated financial conditions and the results of operations of Borrower as
of, and for the portion of the fiscal year ending on, the date or dates thereof.
There were no material adverse events or liabilities, direct or indirect, fixed
or contingent, of Borrower as of the date or dates of such financial statements
and known to Borrower, which are not reflected therein or in the notes thereto.
Except for transactions directly related to, or

<PAGE>

specifically contemplated by, the Loan Documents and transactions heretofore
disclosed in writing to Lender, there have been no material adverse changes in
the respective financial conditions of Borrower and/or its Subsidiaries from
those shown in such financial statements between such date or dates and the date
hereof.

         3.11  Taxes. All federal, state, foreign, and other Tax returns of
               -----
Borrower and each Subsidiary required to be filed have been filed, and all
federal, state, foreign, and Taxes are shown thereon as owing have been paid.
Borrower does not know of any pending audit or investigation of Borrower and/or
any Subsidiary with any taxing authority.

         3.12  Title to Collateral. Borrower owns, and with respect to
               -------------------
Collateral delivered after the date hereof, Borrower will own, legally and
beneficially, the Collateral free of any lien or claim or any right or option on
the part of any third person to purchase or otherwise acquire the Collateral or
any part thereof, except for the first priority lien granted pursuant to the
Loan Documents. The Collateral is not subject to any restriction on transfer or
assignment except for compliance with applicable federal and state laws and
regulations promulgated thereunder. Borrower has the unrestricted right to
pledge the Collateral as contemplated hereby. All of the Collateral has been,
and with respect to Collateral delivered after the date hereof, will be duly and
validly issued and fully paid and nonassessable.

         3.13  Use of Loan Proceeds. All loan proceeds or funds furnished by
               --------------------
Lender to Borrower pursuant to this Agreement shall be used solely for the
purpose specified in Article II of this Agreement.

                                   ARTICLE IV

                              Affirmative Covenants
                              ---------------------

         While any part of the Obligations remains unpaid and unless otherwise
waived in writing by Lender:

         4.01  Accounts, Reports and Other Information. Borrower shall maintain,
               ---------------------------------------
and cause each Subsidiary to maintain, a standard system of accounting in
accordance with regulatory accounting principles or GAAP, as applicable, and
Borrower shall furnish to Lender the following:

<PAGE>

          (a)  Quarterly Statements. As soon as available, but no more than
               --------------------
     forty-five (45) days after the end of each quarter of Borrower's fiscal
     year (except for the last quarter), (i) the balance sheet of the Borrower
     as of the last day of such quarter; (ii) statements of income and retained
     earnings of Borrower for the quarter; (iii) an officer's certificate
     setting forth the information required to establish whether Borrower and
     Summit Bank, N.A. were in compliance with the financial covenants and
     ratios set forth in Article V hereof during the period covered and that
     signer or signers have reviewed the relevant terms in this Agreement and
     have made, or caused to be made under their supervision, a review of the
     transactions of Bank from the beginning of the accounting period covered by
     the financial statements being delivered therewith to the date of the
     officer's certificate and that such review has not disclosed any Event of
     Default, or material violation or breach in the due observance of any
     covenant, agreement or provision of this Agreement; (iv) upon receipt by
     Borrower, copies of the Uniform Bank Performance Report for Bank prepared
     by the Federal Financial Institutions Examination Council; (v) a copy of
     the Borrower's 10Q; (vi) copies of the Federal Reserve Forms Y-9C and Y-9LP
     for the Borrower, (vii) copies of all FFIEC Call Reports furnished by Bank
     to the appropriate Tribunal. and (viii) such other information as Lender
     shall reasonably request.

          (b)  Annual Audit. As soon as available, but no more than one hundred
               ------------
     twenty (120) days after the end of each fiscal year of Borrower: (i) copies
     of consolidated balance sheets, statements of income and retained earnings
     and statement of cash flows of Borrower, setting forth in each case, in
     comparative form, figures for the previous fiscal year, all in reasonable
     detail; and (ii) if requested by Lender, an opinion by an independent
     certified public accountant selected by Borrower, and acceptable to Lender,
     which opinion shall state that said consolidated financial statements have
     been prepared in accordance with GAAP and that such accountant's audit of
     such financial statements has been made in accordance with generally
     accepted auditing standards and that said financial statements present
     fairly the consolidated financial condition of Borrower and Bank and the
     results of their operations; (iii) a copy of the Borrower's 10K; (iv) copy
     of the Federal Reserve Board Form Y-6 Annual Report of Borrower, as filed
     with the Board of Governors of the Federal Reserve System; and (v) such
     other information as Lender may reasonably request.

          (c)  Other Reports and Information. As soon as available, copies of
               -----------------------------
     all other financial and other statements, reports, correspondence, notices
     and information of Borrower, each Subsidiary as may be requested, in form
     and substance reasonably satisfactory to Lender, including, but not limited
     to, and subject to any requirements of confidentiality, copies of all
     written communications of Borrower or any Subsidiary with any regulatory
     authority, a copy of any third party loan review, a written summary of the
     management recap of any regulatory examinations and/or visitations, a copy
     of the internal Allowance for Loan and Lease Losses (ALLL) Policy and shall
     at least quarterly

<PAGE>

         submit a copy or written summary of their internal evaluation
         of ALLL adequacy and the Borrower shall add Lender to its shareholder
         mailing list which will allow it to receive copies of correspondence
         with its shareholders.

         4.02  Existence. Borrower and its Subsidiaries shall maintain their
               ---------
respective existence as a corporation and all of its privileges, franchises,
agreements, qualifications and rights that are necessary or desirable in the
ordinary course of business; and Borrower shall cause each of its Subsidiaries
to maintain and preserve their respective good standing with all Tribunals.

         4.03  Observance of Terms. Borrower shall: (i) pay the principal and
               -------------------
interest on the Notes in accordance with its terms; and (ii) observe, perform,
and comply with every covenant, term and condition herein expressed or implied
on the part of Borrower to be observed, performed or complied with.

         4.04  Compliance With Applicable Laws. Borrower and each Subsidiary
               -------------------------------
shall in all material respects comply with the requirements of all applicable
Laws of any Tribunal.

         4.05  Inspection. Borrower and each Subsidiary shall permit any
               ----------
representatives of Lender to visit, review and/or inspect any of its properties
and assets at any reasonable time and to examine all books of account, records,
reports, examinations and other papers (subject to applicable confidentiality
requirements), to make copies therefrom at the expense of Borrower, and to
discuss the affairs, finances and accounts of Borrower and each Subsidiary with
their respective employees and officers at all such reasonable times and as
often as may be reasonably requested.

         4.06  Change. Borrower shall promptly notify Lender of: (i) all
               ------
litigation affecting Borrower which is not adequately covered by insurance and
which could have a material adverse effect on the financial condition or
operations of the Borrower; (ii) any other matter which could have a material
adverse effect on the financial condition or operations of Borrower.

         4.07  Payment of Taxes. Borrower and its Subsidiaries shall pay all
               ----------------
lawful Taxes imposed upon them or upon their income or profits or upon any of
their property before the same shall be delinquent; provided, however, that
neither Borrower nor any Subsidiary shall be required to pay and discharge any
such Taxes: (i) so long as the validity thereof shall be contested in good faith
by appropriate proceedings diligently pursued and such liable party shall set
aside on its books adequate reserves with respect thereto and shall pay any such
Taxes before any of its property shall be sold to satisfy any lien which has
attached as a security therefor; and (ii) if Lender has been notified of such
proceedings.

         4.08  Insurance. Borrower and each Subsidiary shall keep all property
               ---------
of a character usually insured by Persons engaged in the same or similar
businesses, adequately insured by financially sound and reputable insurers, and
shall furnish Lender evidence of such insurance immediately upon request in form
satisfactory to Lender.

<PAGE>

         4.09  Compliance With ERISA. Borrower and each Subsidiary shall comply,
               ---------------------
if applicable, in all material respects, with the provisions of the Employee
Retirement Income Security Act of 1974, as amended, and furnish to Lender, upon
Lender's request, such information concerning any plan of Borrower or Bank
subject to said Act as may be reasonably requested. Borrower and each Subsidiary
shall notify Lender immediately of any fact or action arising in connection with
any plan which might constitute grounds for the termination thereof by the
Pension Benefit Guaranty Corporation or for the appointment by the appropriate
United States district court of a trustee or administrator for such plan.

         4.10  Financial Condition. Subject to the provisions of Article V,
               -------------------
Borrower shall cause Bank to maintain the ratios of loans to deposits, loan loss
reserves and liquidity at percentages acceptable to all Tribunals having
jurisdiction over Bank.

         4.11  Maintenance of Priority of Liens. Borrower and each Subsidiary
               --------------------------------
shall each perform such acts and shall duly authorize, execute, acknowledge,
deliver, file, and record such additional assignments, security agreements, and
other agreements, documents, instruments, and certificates as Lender may deem
reasonably necessary or appropriate in order to perfect and maintain the
security interest created in favor of Lender in the Security Instruments.

         4.12  FDIC Insurance. Borrower shall cause the Bank to maintain federal
               --------------
deposit insurance and to be a member of the Federal Deposit Insurance
Corporation.

         4.13  Notices. Borrower shall promptly notify, and shall cause each
               -------
Subsidiary to promptly notify, Lender of (i) the occurrence of an Event of
Default, or of any event that with notice or lapse of time or both would be an
Event of Default, (ii) the commencement of any action, suit, or proceeding
against Borrower or any Subsidiary that might in the reasonable judgment of
Borrower have a material adverse effect on the business, financial condition, or
operations of Borrower or any Subsidiary, and (iii) any other matter that might
in the reasonable judgment of Borrower have a material adverse effect on the
business, financial condition, or operations of Borrower or any Subsidiary.

                                    ARTICLE V

                               Negative Covenants
                               ------------------

         While any part of the Obligations remains unpaid and unless waived in
writing by Lender:

         5.01  Capital Ratio. The Borrower shall not permit the Capital Ratio of
               -------------
Bank to at any time be less than six percent (6.0%), calculated quarterly.

<PAGE>

         5.02  Non-Performing Loans Ratio. The Borrower shall not permit the
               --------------------------
Bank's Non-Performing Loans Ratio to at any time be less than one-hundred
(100.0%).

         5.03  Return on Average Assets. The Borrower shall not permit the
               ------------------------
Bank's annual Return on Average Assets to at any time be less than one and
two-tenths percent (1.2%).

         5.04  Tangible Net Worth. The Borrower shall not permit its
               ------------------
consolidated Tangible Net Worth to at any time be less than Forty-Five Million
and no/100 Dollars ($45,000,000.00).

         5.05  Cash Flow Coverage. The Borrower shall maintain at all times a
               ------------------
Cash Flow Coverage of not less than 1.5 to 1.0, calculated on a quarterly
annualized basis.

         5.06  Return on Equity Capital. The Borrower shall cause the Bank to at
               ------------------------
all times maintain an annual Return on Equity Capital of not less than ten
percent (10%).

         5.07  Bad Debt Ratio. The Borrower shall not permit the Bad Debt Ratio
               --------------
to at any time be less than one percent (1%).

         5.08  Dividends. Borrower shall not declare or pay any dividends, make
               ---------
any payment on account of any class of the capital stock of Borrower now or
hereafter outstanding, or make any distribution of cash or property to holders
of any shares of such stock which exceed $4,000,000.00 in the aggregate during
any fiscal year, provided however, without Lender's prior written consent,
Borrower will not declare any dividend so long as Borrower is in default in
payment of the Obligations. Payment by Borrower for shares purchased under a
stock repurchase plan by which Borrower purchases its own shares on the open
market will not be considered a distribution to shareholders.

         5.09  Business. Borrower and each Subsidiary shall not engage, directly
               --------
or indirectly, in any business other than the businesses permitted by statute
and the regulations of the appropriate governmental and regulatory agencies or
Tribunals.

         5.10  Other Liens, Disposition of Assets. Borrower or any Subsidiary
               ----------------------------------
shall not create or suffer to exist a lien or security interest upon, or
otherwise dispose of or encumber, any Collateral securing Borrower's payment and
performance of the Obligations, nor will Borrower or any Subsidiary sell, lease,
or otherwise dispose of any material part of their assets or investments, except
in the ordinary course of business.

         5.11  Limitation on Debt. Borrower shall not, nor allow any Subsidiary
               ------------------
to, create, incur, assume, become liable in any manner in respect of, or suffer
to exist, any debt for borrowed money except:

               (a)  debt, excluding debt created under this Agreement, not in
         excess of $1,000,000.00 at any one time outstanding;

<PAGE>

               (b)  debt created under this Agreement;

               (c)  debt secured by a purchase money security interest; and

               (d)  $25,000,000.00 of federal funds purchased; and

               (e)  any borrowings from the Federal Home Loan Bank which shall
                    not exceed $50,000,000.

         5.12  Prepayment of Debt. Borrower shall not, and Borrower shall not
               ------------------
permit its Subsidiaries to prepay any of their respective material debt, other
than the debt created under this Agreement, or incurred in the ordinary course
of business before the same becomes due.

         5.13  Issuance of Stock. No Subsidiary shall authorize or issue shares
               -----------------
of stock of any class, common or preferred, or any warrant, right or option
pertaining to its capital stock or issue any security convertible into capital
stock, except for any issued to Borrower by any Subsidiary of Borrower, provided
however, any stock issued by a Bank shall be pledged to Lender.

                                   ARTICLE VI

                                     Default
                                     -------

         6.01  Events of Default.  Each of the following shall be deemed an
               -----------------
"Event of Default":

               (a) Failure by Borrower to pay or perform any part or component
         of the Obligations, when due or declared due and continuation of such
         failure for a period of three (3) Business Days thereafter; or,

               (b) Any representation or warranty made or deemed made by
         Borrower or any other Person in any Loan Documents, or in any
         certificate or financial or other statement furnished at any time to
         Lender by or on behalf of Borrower shall be false, misleading or
         erroneous in any material respect as of the date made, deemed made, or
         furnished and failure by Borrower to cure the same within thirty (30)
         days after notice thereof is given by Lender to Borrower; or,

               (c) Failure to observe, perform or comply with any of the
         covenants, terms, or agreements contained in this Agreement or any
         other Loan Document and failure by Borrower to cure the same within
         thirty (30) days after notice thereof is given by Lender to Borrower;
         or,

               (d) Failure by Borrower or any Subsidiary to pay any of its
         material indebtedness as the same becomes due or within any applicable
         grace period (other than

<PAGE>

         indebtedness being actively contested in good faith and for which
         adequate reserves have been established in accordance with generally
         accepted accounting principles); or,

                  (e) Borrower or any Subsidiary shall file a petition for
         bankruptcy, liquidation or any answer seeking reorganization,
         rearrangement, readjustment of its debts or for any other relief under
         any applicable bankruptcy, insolvency, or similar act or law, now or
         hereafter existing, or any action consenting to, approving of, or
         acquiescing in, any such petition or proceeding; or the appointment by
         consent or acquiescence of, a receiver, trustee, liquidator, or
         custodian for all or a substantial part of its property; or the making
         of an assignment for the benefit of creditors; or the inability to pay
         its debts as they mature; or take any corporate action to authorize any
         of the foregoing; or,

                  (f) Filing of an involuntary petition against Borrower or any
         Subsidiary seeking reorganization, rearrangement, readjustment or
         liquidation of its debts or for any other relief under any applicable
         bankruptcy, insolvency or other similar act or law, now or hereafter
         existing, or the involuntary appointment of a receiver, trustee,
         liquidator or custodian of all or a substantial part of its property,
         and such involuntary proceeding or appointment remains unvacated,
         undismissed or unstayed for a period of ninety (90) days; or the
         issuance of a writ of attachment, execution, sequestration or similar
         process against any part of its property and same remains unbonded,
         undischarged, or undismissed for a period of thirty (30) days from the
         date of notice; or,

                  (g) Final judgment for the payment of money in excess of
         $100,000.00 shall be rendered against Borrower or any Subsidiary and
         the same shall remain undischarged for a period of thirty (30) days
         during which execution shall not be effectively stayed; or,

                  (h) An event occurs which has a material adverse affect on the
         financial conditions or operation of Borrower or Summit Bank, N.A.;
         or,


                  (i) A change in control of Summit Bank, N.A. (as such or
         similar term is used in the Texas Banking Code of 1943 and in the
         Financial Institutions Regulatory and Interest Rate Control Act) shall
         occur, or action to change such control shall be commenced, without the
         prior written consent of Lender (which consent may be given or withheld
         in Lender's sole discretion); or,

                  (j) This Agreement or any other Loan Document shall be
         declared null and void or the validity or enforceability thereof shall
         be contested or challenged by Borrower or any Subsidiary or Borrower
         shall deny that it has any further liability or obligation under any of
         the Loan Documents; or,

                  (k) Receipt by Bank of a notice from the Federal Deposit
         Insurance Corporation of intent to terminate status as an insured
         bank; or,

<PAGE>

              (l) The filing by Bank of an application for relief pursuant to
         section 13(c) of 13(i) of the Federal Deposit Insurance Act, as
         amended, or similar relief from any Tribunal; or,

              (m) The filing by Bank of an application for capital forbearance
         from any Tribunal; or,

              (n) If Lender shall have elected to file any financing statement
         with respect to the Collateral, Lender shall receive at any time
         following the execution of this Agreement a search report indicating
         that Lender's security interest in the Collateral is not prior to all
         other security interests or other interests reflected in the report and
         Borrower has failed to cure such default by having a termination
         statement filed for such prior lien within thirty (30) days after
         notice thereof is given by Lender to Borrower.

         6.02 Remedies Upon Default. Upon the occurrence of any Event of Default
              ---------------------
set forth in Section 6.01, at the option of Lender, the obligation of Lender to
extend credit to Borrower pursuant hereto shall immediately terminate and the
principal of and interest accrued on the Notes if not earlier demanded, shall be
immediately and automatically forthwith DEMANDED and due and payable without any
notice or demand of any kind, and the same shall be due and payable immediately
without any notice, presentment, acceleration, demand, protest, notice of
acceleration, notice of intent to accelerate, notice of intent to demand, notice
of protest or notice of any kind (except notice required by law which has not
been waived herein), all of which are hereby waived. Upon the occurrence of any
Event of Default, Lender may exercise all rights and remedies available to it in
law or in equity, under any Loan Document or otherwise.

                                   ARTICLE VII

                                  Miscellaneous
                                  -------------

         7.01 Notices. Unless otherwise provided herein, all notices, requests,
              -------
consents and demands shall be in writing and delivered in person or mailed,
postage prepaid, certified mail, return receipt requested, addressed as follows:

         If intended for Borrower or its Subsidiaries, to:

              SUMMIT BANCSHARES, INC.
              1300 Summit, Suite 604
              Fort Worth, Texas 76102
              Attn: Philip E. Norwood

<PAGE>

         If intended for Lender, to:

                  THE FROST NATIONAL BANK
                  100 West Houston Street
                  P.O. Box 1600
                  San Antonio, Texas 78296
                  Attn: Jerry L. Crutsinger


or to such other person or address as either party shall designate to the other
from time to time in writing forwarded in like manner. All such notices,
requests, consents and demands shall be deemed to have been given or made when
delivered in person, or if mailed, when deposited in the mails.

         7.02 Place of Payment. All sums payable hereunder to Lender shall be
              ----------------
paid at Lender's banking office at 100 West Houston Street, P.O. Box 1600, San
Antonio, Texas 78296. If any payment falls due on other than a Business Day,
then such due date shall be extended to the next succeeding Business Day, and
such amount shall be payable in respect to such extension.

         7.03 Survival of Agreement. All covenants, agreements, representations
              ---------------------
and warranties made in this Agreement shall survive the execution and delivery
of this Agreement in the making of the Loan. All statements contained in any
certificate or other instrument delivered by Borrower hereunder shall be deemed
to constitute representations and warranties made by Borrower.

         7.04 No Waiver. No waiver or consent by Lender with respect to any act
              ---------
or omission of Borrower or any Subsidiary on one occasion shall constitute a
waiver or consent with respect to any other act or omission by Borrower or any
Subsidiary on the same or any other occasion, and no failure on the part of
Lender to exercise and no delay in exercising any right hereunder shall operate
as a waiver thereof, nor shall any single or partial exercise by Lender of any
right hereunder preclude any other or further right of exercise thereof or the
exercise of any other right. The rights and remedies provided for in this
Agreement and the other Loan Documents are cumulative and not exclusive of any
rights and remedies provided by Law.

         7.05 Accounting Terms. All accounting and financial terms used herein,
              ----------------
and the compliance with each covenant herein which relates to financial matters,
shall be determined in accordance with regulatory accounting principles or GAAP.

         7.06 Lender Not In Control. None of the covenants or other provisions
              ---------------------
contained in the Agreement shall, or shall be deemed to, give Lender the right
or power to exercise control over the affairs and/or management of Borrower or
any Subsidiary, the power of Lender being limited to those rights generally
given to lenders; provided that, if Lender becomes the owner of any stock or
other equity interest in Borrower or any Subsidiary whether through foreclosure
or

<PAGE>

otherwise, Lender shall be entitled to exercise such legal rights as it may have
by being an owner of such stock, or other equity interest in Borrower or any
Subsidiary.

         7.07 Joint Venture, Partnership, Etc. None of the covenants or other
              -------------------------------
provisions contained in this Agreement shall, or shall be deemed to, constitute
or create a joint venture, partnership or any other association, affiliation, or
entity between Borrower or any Subsidiary and Lender.

         7.08 Successors and Assigns. All covenants and agreements contained in
              ----------------------
this Agreement and all other Loan Documents shall bind and inure to the benefit
of the respective successors and assigns of the parties hereto, except that
neither Borrower nor any Subsidiary may assign its rights herein, in whole or in
part.

         7.09 Expenses. Borrower agrees to reimburse Lender for its
              --------
out-of-pocket expenses, including reasonable attorneys' fees, in connection with
the negotiation, preparation, administration and enforcement of this Agreement
or any of the Loan Documents, making the Loan hereunder, and in connection with
amendments, consents and waivers hereunder.

         7.10 Governing Law. THIS AGREEMENT, THE NOTE, AND ALL OTHER LOAN
              -------------
DOCUMENTS SHALL BE DEEMED CONTRACTS UNDER THE LAWS OF THE STATE OF TEXAS AND
SHALL BE CONSTRUED AND ENFORCED IN ACCORDANCE WITH AND GOVERNED BY THE LAWS OF
THE STATE OF TEXAS, EXCEPT TO THE EXTENT THAT FEDERAL LAWS MAY APPLY. THIS
AGREEMENT, THE NOTES AND THE OTHER LOAN DOCUMENTS SHALL BE DEEMED TO HAVE BEEN
MADE AND TO BE PERFORMED IN SAN ANTONIO, BEXAR COUNTY, TEXAS.

         7.11 Severability. If any provision of this Agreement is held to be
              ------------
illegal, invalid or unenforceable under present or future Laws effective during
the term of this Agreement, such provision shall be fully severable; this
Agreement shall be construed and enforced as if such illegal, invalid and
unenforceable provision had never comprised a part of this Agreement; and
remaining provisions of this Agreement shall remain in full force and effect and
shall not be affected by the illegal, invalid or unenforceable provision or by
its severance from this Agreement.

         7.12 Modification or Waiver. No modification or waiver of any provision
              ----------------------
of this Agreement, the Note, or any Loan Documents shall be effective unless
such modification or waiver shall be in writing and executed by a duly
authorized officer of Lender.

         7.13 Right of Setoff. Nothing in this Agreement shall be deemed a
              ---------------
waiver of Lender's right of Lender's banker's lien or setoff.

         7.14 Release. Lender will not be liable to Borrower for any claim
              -------
arising from or relating to any of the Loan Documents or any transactions
contemplated thereby except upon proof of Lender's gross negligence or wilful
misconduct or wilful breach of its agreements.

<PAGE>

         7.15 Waiver of DTPA. Neither the Borrower nor its Subsidiary is in a
              --------------
significantly disparate bargaining position and they have both been represented
by legal counsel in this transaction. The Borrower and its Subsidiaries hereby
waive the applicability of the Texas Deceptive Trade Practices Act (other than
ss.17.555) to the transaction and any and all rights or remedies that may be
available to the Borrower or any Subsidiary in connection with this transaction.

         7.16 Counterparts. This Agreement may be executed simultaneously in
              ------------
multiple counterparts, all of which together shall constitute one and the same
instrument.

         7.17 Headings. The headings, captions, and arrangements used in this
              --------
Agreement are for convenience only and shall not affect the interpretation of
this Agreement.

         7.18 Maximum Interest Rate. No provision of this Agreement or of the
              ---------------------
Notes shall require the payment or the collection of interest in excess of the
maximum permitted by applicable law. If any excess of interest in such respect
is hereby provided for, or shall be adjudicated to be so provided, in the Notes
or otherwise in connection with this loan transaction, the provisions of this
Section 7.18 shall govern and prevail and Borrower shall not be obligated to pay
the excess amount of such interest or any other excess sum paid for use,
forbearance, or detention of sums loaned pursuant hereto. In the event Lender
ever receives, collects, or applies as interest any such sum, such amount which
would be in excess of the maximum amount permitted by applicable law shall be
applied as a payment and reduction of the principal of the indebtedness
evidenced by the Note; and, if the principal of the Notes has been paid in full,
any remaining excess shall forthwith be paid to Borrower.

         7.19 Assignment, Participation, or Pledge by Lender. Lender may from
              ----------------------------------------------
time to time, without notice to Borrower: (i) pledge or encumber or assign to
any one or more Persons (including, but not limited to, one or more of Lender's
affiliates, subsidiaries, or subsidiaries of Lender's affiliates) all of
Lender's right, title and interest in and to this Agreement, the Loan Documents
and/or the collateral securing the Loan; or (ii) sell, to any one or more
Persons, a participation or joint venture interest in all or any part of
Lender's right, title, and interest in and to this Agreement, the Loan Documents
and/or such collateral; and Borrower hereby expressly consent to any such future
transaction. Each participant or joint venturer shall be entitled to receive all
information regarding the creditworthiness of Borrower, including, without
limitation, all information required to be disclosed to a participant or joint
venturer pursuant to any Law of any Tribunal.

         7.20 Confidentiality. The Lender agrees to keep in confidence all
              ---------------
records and information provided by Borrower to Lender which is marked or
identified as confidential. Lender agrees not to use the records and information
provided by Borrower to Lender to solicit customers of Borrower or any of its
Subsidiaries or to gain any competitive advantage against Borrower or any of its
Subsidiaries.

<PAGE>

         7.21 ENTIRE AGREEMENT. THIS AGREEMENT AND THE OTHER LOAN DOCUMENTS
              ----------------
CONSTITUTE THE ENTIRE AGREEMENT, UNDERSTANDING, REPRESENTATIONS AND WARRANTIES
OF THE PARTIES HERETO AND SUPERSEDE ALL PRIOR AGREEMENTS, ARRANGEMENTS AND
UNDERSTANDINGS BETWEEN THE PARTIES. THERE ARE NO ORAL AGREEMENTS BETWEEN THE
PARTIES. SHOULD A CONFLICT IN ANY TERMS, CONDITIONS OR COVENANTS EXIST BETWEEN
THIS AGREEMENT AND ANY OF THE LOAN DOCUMENTS, THIS AGREEMENT SHALL BE
CONTROLLING.

         IN WITNESS HEREOF, Borrower and Lender, by and through their duly
authorized officers, have caused this Agreement to be executed the day and year
first above written.

BORROWER:                 SUMMIT BANCSHARES, INC.


                                 By: /s/  Philip E. Norwood
                                     -------------------------------------------
                                     Philip E. Norwood, Chairman and President


LENDER:                          THE FROST NATIONAL BANK

                                 By: /s/ Jerry L. Crutsinger
                                     -------------------------------------------
                                     Jerry L. Crutsinger, Senior Vice President