<PAGE>


                                                                   EXHIBIT 10(a)



                            COMMERCE BANCSHARES, INC.

                      EXECUTIVE INCENTIVE COMPENSATION PLAN

                   AMENDMENT AND RESTATEMENT OF JULY 31, 1998



1.       PURPOSE

         The policy of Commerce Bancshares, Inc. ("Commerce") is to compensate
its officers based on performance. The purpose of this Executive Incentive
Compensation Plan ("Plan") is to provide incentive compensation awards to those
individuals whose management efforts reflect a desire to meet commonly agreed
upon objectives or to those who by their superior performance directly
contribute to the profitability of Commerce and to encourage the retention of
outstanding contributors.

         This Plan is intended to comply with Section 162(m) of the Internal
Revenue Code (the "Code") so that awards made under the Plan to individuals who
are covered employees within the meaning of Code Section 162(m)(3) ("Covered
Employees") will qualify as performance-based compensation within the meaning of
Code Section 162(m) and the regulations thereunder ("Performance-Based
Compensation").

2.       ADMINISTRATION

         The Plan shall be administered by the Compensation and Benefits
Committee ("Committee") of the Board of Directors ("Board") of Commerce, which
shall consist solely of two or more directors who are "non-employee directors"
under Rule 16b-3(b)(3) promulgated under the Securities Exchange Act of 1934, as
amended, or any successor provision thereto, and "outside directors" within the
meaning of Treasury Regulation Section 1.162-27(e)(3)(i). The Committee shall
have authority in its sole discretion to interpret the Plan, establish rules and
procedures thereunder, and make all determinations, including the determination
of incentive compensation awards eligible to be deferred under the Plan. All
determinations made by the Committee shall be final and binding.

3.       ELIGIBLE PARTICIPANTS

         All chief executive officers, Chairman of the Board, Presidents, and
Vice Presidents of Commerce or any of its affiliated banks or subsidiary
companies shall be eligible to participate in the Plan, together with such other
officers of Commerce and its affiliated banks and subsidiary companies as the
Committee shall determine. Directors who are not officers or employees of
Commerce, an affiliated bank, or a subsidiary company, are not eligible to
participate in the Plan.

<PAGE>

4.       DETERMINATION OF AWARD

         The Board of Commerce in its sole discretion shall approve the amount
of the aggregate incentive compensation awards to be granted based on the
recommendation of the Committee. Individual incentive compensation awards shall
be granted in the following manner:

         a.   With respect to Covered Employees, individual incentive
              compensation awards shall qualify as Performance-Based
              Compensation. In so qualifying awards, the Committee, in its sole
              discretion, may set restrictions based upon the achievement of
              objective performance goals within the meaning of Code Section
              162(m) and the regulations thereunder ("Performance Goals"). Each
              award to a Covered Employee shall meet the following requirements:

                (i) Performance Goals for the award shall be established by the
                    Committee based on one or more of the following criteria:
                    revenue, earnings, earnings per share, pre-tax earnings and
                    net profits, stock price, market share, costs, return on
                    equity, efficiency ratio (non-interest expense, divided by
                    total revenue) asset management, asset quality, asset growth
                    and budget achievement. Performance Goals need not be the
                    same with respect to all Covered Employees and may be
                    established separately for Commerce as a whole or for its
                    various groups, divisions, subsidiaries and affiliates.

               (ii) Each Performance Goal shall be specifically defined in
                    advance by the Committee and may include or exclude
                    specified items of an unusual, non-recurring or
                    extraordinary nature.

              (iii) Each Performance Goal must be sufficiently objective that a
                    third party having knowledge of the relevant facts could
                    determine whether the Performance Goal has been met.

               (iv) Different awards may be set by the Committee based on
                    achievement of certain Performance Goals or specified levels
                    of achieving the Performance Goals. However, no award shall
                    be paid to any Covered Employee if the applicable minimum
                    Performance Goal(s) are not achieved.

                (v) Performance Goals shall be set by the Committee before the
                    end of the period that constitutes the first twenty-five
                    percent (25%) of the period of service to which the
                    Performance Goal relates, provided that the outcome is
                    substantially uncertain at the time the Committee actually
                    establishes the Performance Goal.

               (vi) The Committee shall have no discretion to increase the
                    amount of compensation that otherwise would be due upon
                    attainment of a Performance Goal, although the Committee may
                    have discretion to deny an award or to adjust downward the
                    compensation payable pursuant to an award, as, in the
                    Committee's sole judgment, is prudent based upon the



                                       2

<PAGE>
                    Committee's assessment of the Covered Employee's performance
                    and Commerce's performance during the Fiscal Year.

              (vii) In granting awards, the Committee shall follow any
                    additional procedures determined by it in its sole
                    discretion from time to time to be necessary, advisable or
                    appropriate to ensure qualification of the awards as
                    Performance-Based Compensation.

         b.   With respect to individuals who are not Covered Employees,
              individual incentive compensation awards shall be determined with
              reference to performance during the preceding year. The incentive
              compensation awards to be made to the Chairman of the Board or the
              President (if such persons are not Covered Employees) shall be
              determined by the Committee. All other awards to be made under
              this Plan may be determined by the Committee, or should the
              Committee so direct, by a committee consisting of the Chief
              Executive Officer, a Vice-Chairman designated by the Chief
              Executive Officer, and the chief human resource officer.

5.       PAYMENT OF INCENTIVE AWARD

         Incentive compensation awards are generally determined and made on or
before the date of the annual meeting of the shareholders of Commerce. The
normal method of payment will be in the form of cash and awards will be paid as
soon as practicable after the awards are determined, provided, that the
recipient of an award shall not have elected to defer receipt of the incentive
compensation award as hereinafter provided.

         Notwithstanding the foregoing, no incentive compensation award shall be
paid to a Covered Employee before the Committee certifies that such Covered
Employee met the requirements of the applicable Performance Goal and satisfied
any other material terms applicable to the incentive compensation award.

         The maximum bonus that may be paid to any employee pursuant to the plan
for any calendar year shall not exceed $1,500,000.

6.       DEFERRAL OPTIONS

         a.   Eligible employees who are members of a select group of management
              or highly compensated employees, as selected by the Commerce
              Director of Human Resources in his or her discretion, may elect to
              defer all or a portion of an incentive compensation award until
              the earlier to occur of retirement, death, or termination. A
              deferral must be expressed either as "all" or as a specified
              dollar amount. Any incentive compensation award above the
              specified amount will be paid in cash, and if the award is less
              than the amount deferred, the total award will be deferred. The
              granting of an incentive compensation award is discretionary and
              neither delivery of deferral election materials nor an election to
              defer shall affect entitlement to such an award. All deferral
              elections made under the Plan are irrevocable. It is intended that
              this arrangement qualify as, and shall be administered to qualify
              as being unfunded and being primarily for the purpose of


                                       3


<PAGE>



              providing deferred compensation for a select group of management
              or highly compensated employees.

         b.   In order to ensure that elections to defer incentive compensation
              awards are effective under applicable tax laws, all persons
              eligible to participate in this Plan will be given the opportunity
              to defer payment of all or a portion of an incentive compensation
              award. An election to defer must be made in a written form
              satisfactory to Commerce and must be received by the Commerce
              Director of Human Resources on or before the last business day of
              the year preceding the year for which performance is measured to
              determine the granting of an incentive compensation award.

         c.   An eligible employee in electing a deferred payment shall also
              elect the accounts, from among the accounts that Commerce makes
              available to the participating employee, to which the relevant
              portion of the award deferral will be credited. Credits to
              available accounts for deferral of an incentive compensation award
              shall be determined from time to time based upon hypothetical
              measuring investments (the "Measuring Investments") for each
              account; one of which shall consist of a Company Stock Account and
              there shall be such other accounts determined from time to time by
              the Director of Human Resources in his or her discretion. Such
              accounts are bookkeeping accounts only and are maintained for the
              sole purpose of determining the amount payable by Commerce to the
              eligible employee based upon the hypothetical performance of the
              Measuring Investments for each such account, determined as if the
              account had assets invested in the Measuring Investments of such
              account. No assets shall be segregated for the benefit of an
              eligible employee and the bookkeeping account shall not represent
              assets set aside for the benefit of an eligible employee.

              With the exception of the Commerce Stock Account, an eligible
              employee may elect to transfer credits between accounts, and the
              amount credited to all such accounts shall be determined from time
              to time, all pursuant to non-discriminatory rules, procedures and
              deadlines set by the Commerce Director of Human Resources, which
              rules, procedures, and deadlines may be amended from time to time
              in such officer's discretion (the "Administrative Rules"). Except
              as set forth in the following paragraph, however, an eligible
              employee may elect to transfer credits into the Commerce Stock
              Account, but not out of the Commerce Stock Account. Any election
              to transfer a credit to the Commerce Stock Account or among the
              other accounts (a "Transfer Election") must be received by the
              Commerce Director of Human Resources by the date set by the
              Commerce Director of Human Resources and must be in a written form
              satisfactory to such officer, in each case pursuant to the
              Administrative Rules. Any transfer to the Commerce Stock Account
              shall be based upon the last sale price of Commerce Stock as
              reported by the National Association of Security Dealers National
              Market System on the last trading day determined in accordance
              with the Administrative Rules. The credit transferred from any
              other account shall be based upon the amount credited to such
              account as of the date determined in accordance with the
              Administrative Rules.

                                       4

<PAGE>


              Notwithstanding the above, an eligible employee may make a
              one-time election to remove any or all amounts out of the Commerce
              Stock Account (a "Diversification Election") as of February 17,
              2000. Such Diversification Election must be made at the time and
              in the manner determined pursuant to the Administrative Rules. Any
              transfer from the Commerce Stock Account shall be based upon the
              last sale price of Commerce Stock as reported by the National
              Association of Security Dealers National Market System on the
              trading day determined in accordance with the Administrative
              Rules. The amount transferred from the Commerce Stock Account
              pursuant to the Diversification Election shall be based upon the
              number of units credited to such account as of the date determined
              in accordance with the Administrative Rules.

         d.   The accounts made available for the deferral of incentive
              compensation awards are bookkeeping accounts. The amount credited
              to each account, including any hypothetical earnings, gains or
              losses, will be determined in accordance with the Administrative
              Rules, based on the investment performance of the Measuring
              Investments for such Account. The timing and manner of making
              credits or debits to each account shall be determined in
              accordance with the Administrative Rules.

         e.   Commerce shall provide periodically to each participant (but not
              less frequently than once per calendar year) a statement setting
              forth the balance to the credit of such participant in each of the
              accounts.

         f.   Amounts deferred under the provisions of this Plan will be
              disbursed to participants in accordance with the following:

                (i) An amount equal to the amounts credited to accounts other
                    than the Commerce Stock Account will be paid by Commerce in
                    a single distribution as soon as reasonably practicable
                    after retirement, disability, death or other termination of
                    employment, except that a participant may elect to instead
                    have payment made in up to ten annual equal installments or
                    in such installments after receiving a lump sum payment of a
                    portion of the payment due. Annual installments will be paid
                    in an amount, less applicable withholding taxes, determined
                    by multiplying the balance in such other accounts by a
                    fraction, the numerator of which is one (1) and the
                    denominator of which is a number equal to remaining unpaid
                    annual installments.

               (ii) If a participant dies after the commencement of payments
                    from such participant's accounts other than the Commerce
                    Stock Account, the designated beneficiary shall receive the
                    remaining installments over the elected installment period.

              (iii) With respect to a participant's Commerce Stock Account, upon
                    such participant's disability, death, retirement, or other
                    termination of employment, Commerce shall transfer to such
                    participant a number of


                                       5

<PAGE>

                    shares of Commerce stock, and cash for any fractional
                    shares, equal to the units credited to the participant's
                    Commerce Stock Account. Alternatively, a participant may
                    elect to have payment with respect to his Commerce Stock
                    Account made in up to ten equal annual installments or in
                    such installments after receiving a lump sum payment of a
                    portion of the payment due, in which case Commerce shall
                    transfer to such electing participant for each installment
                    the number of shares of Commerce stock, and cash for any
                    fractional shares, equal to the units credited to the
                    portion of the participant's Commerce Stock Account to be
                    paid in such installment. No payment, however, shall be made
                    with respect to the Commerce Stock Account until
                    arrangements satisfactory to Commerce shall have been made
                    to provide for payment to Commerce of federal, state, local,
                    and payroll withholding taxes attributable to such payment.

               (iv) Each participant shall have the right at any time to
                    designate any person or persons as beneficiary or
                    beneficiaries (both principal as well as contingent) to whom
                    payment under this Plan shall be made in the event of death
                    prior to complete distribution to the participant of the
                    amounts due under this Plan. Any beneficiary designation may
                    be changed by a participant by the filing of such change in
                    writing on a form prescribed by Commerce. The filing of a
                    new beneficiary designation form will cancel all beneficiary
                    designations previously filed and will apply to all
                    deferrals in the account. If a beneficiary has not been
                    designated or if all designated beneficiaries predecease the
                    participant, then any amounts payable to the beneficiary
                    shall be paid to the participant's estate in one lump sum.

                (v) If there is any change in the number or class of shares of
                    Commerce stock through the declaration of stock dividend or
                    other extraordinary dividends or recapitalization resulting
                    in stock splits or combinations or exchanges of such shares
                    or in the event of similar corporate transactions, each
                    participant's Commerce Stock Account shall be equitably
                    adjusted to reflect any such change in the number or class
                    of issued shares of common stock of Commerce or to reflect
                    such similar corporate transaction.

               (vi) The Human Resources/Salary Committee of Commerce, upon 30
                    days written notice, may approve a "hardship" request for
                    distribution of a deferred award. Unless the participant
                    presents proof satisfactory to such committee of financial
                    need, requests for hardship distribution will be denied.
                    Each request will be evaluated on the basis of uniformly
                    applied criteria.

7.       AMENDMENT AND TERMINATION OF PLAN

         The Board of Directors may at its discretion and at any time amend the
Plan in whole or in part. The Committee may terminate the Plan in its entirety
at any time, and, upon such termination or such later date or dates, each
participant shall: receive, in a single distribution, the shares and cash for
the fractions thereof of Commerce Stock credited to the Commerce Stock


                                       6


<PAGE>

Account; and shall be paid, in a single distribution or over such period of time
as determined by the Committee, an amount equal to the then remaining amount
credited to such participant's accounts other than the Commerce Stock Account.

8.       MISCELLANEOUS

         a.   A participant under this Plan is merely a general unsecured
              creditor and nothing contained in this Plan shall create a trust
              of any kind or a fiduciary relationship between Commerce and the
              participant or the participant's estate. Nothing contained herein
              shall be construed as conferring upon the participant the right to
              continued employment with Commerce or its subsidiaries or to an
              incentive compensation award. Except as otherwise provided by
              applicable law, benefits payable under this Plan may not be
              assigned or hypothecated, and no such benefits shall be subject to
              legal process or attachment for the payment of any claim of any
              person entitled to receive the same.

         b.   The amendment of the Plan to allow a Commerce Stock deferral
              option shall become effective on the date the shareholders of
              Commerce approve the same. Subject to such approval, an employee
              having a deferred option may elect (but prior to June 30, 1994) to
              transfer his balance in the Treasury Bill account and/or the
              Treasury Note Account as of April 1, 1994 to the Commerce Stock
              Account with the number of units credited to his account
              determined as provided in Section 6d hereof but based on the last
              sale price as of the last day in March 1994 on which a trade of
              Commerce Stock is reported. An employee who in 1993 deferred a
              potential incentive compensation award with respect to performance
              in 1994 and elected either a Treasury Bill Account or a Treasury
              Note Account may elect prior to June 30, 1994 to defer such award
              for 1994 to the Common Stock Account.

         c.   Notwithstanding any other provision herein, Commerce may establish
              a trust subject to the claims of the general creditors of Commerce
              (a "rabbi trust") and deposit amounts into the rabbi trust.
              Although any payments from the rabbi trust to a participant shall
              discharge Commerce's obligation to the extent of payment made,
              this plan is unfunded and no participant shall have an interest in
              any rabbi trust asset.

         d.   Notwithstanding any other provision of this Plan to the contrary,
              incentive compensation awards shall not be paid to Covered
              Employees unless and until the material terms under which the
              remuneration is to be paid, including the Performance Goals, are
              (1) disclosed to shareholders and (2) subsequently approved by a
              majority of the vote in a separate shareholder vote before the
              payment of such remuneration.


                                       7