<PAGE>   1

                                 EXHIBIT 10(f)
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                                                                   Exhibit 10(f)

                          SALARY CONTINUATION AGREEMENT

         THIS AGREEMENT is effective this 1st day of December, 1999, by and
between SOUTHSIDE BANCSHARES CORP. (the "Company"), with its principal place of
business in St. Louis, Missouri, and THOMAS M. TESCHNER (the "Executive").

                                  INTRODUCTION

         To encourage the Executive to remain an employee of the Company, the
Company is willing to provide salary continuation benefits to the Executive. The
Company will pay the benefits from its general assets.

                                    AGREEMENT

         The Executive and the Company agree as follows:

                                   ARTICLE 1
                                  DEFINITIONS

         1.1. Definitions. Whenever used in this Agreement, the following words
and phrases shall have the meanings specified:

                  1.1.1. "Change of Control" shall be deemed to have occurred as
of the first day any one more of the following conditions shall have been
satisfied:

                  (a) Any individual, corporation (other than the Company),
         partnership, trust, association, pool, syndicate, or any other entity
         or any group of persons (other than the Southside Bancshares Corp.1993
         Non-Qualified Employees Stock Ownership Plan) acting in concert becomes
         the beneficial owner, as that concept is defined in Rule 13d-3
         promulgated by the Securities and Exchange Commission under the
         Securities Exchange Act of 1934, as amended, of the securities of the
         Company possessing fifty percent (50%) or more of the voting power for
         the election of directors of the Company;

                  (b) There shall be consummated any consolidation, merger or
         other business combination involving the Company or the securities of
         the Company in which holders of voting securities of the Company, as
         the case may be, immediately prior to such consummation own, as a
         group, immediately after such consummation, voting securities of the
         Company, as the case may be (or if the Company does not survive such
         transaction(s), voting securities of the corporation(s) surviving such
         transaction(s)) having less than fifty percent (50%) of the total
         voting power in an election of the directors of the Company (or such
         other surviving corporation (s));

                  (c) During any period of two (2) consecutive years,
         individuals who at the beginning of such period constitute the
         directors of the Company cease for any reason to constitute at least a
         majority thereof;
<PAGE>   3
                  (d) Removal by the stockholders of the Company of all or a
         majority of the incumbent directors of the Company; or

                  (e) There shall be consummated any sale, lease, exchange, or
         other transfer (in one transaction or a series of related transactions)
         of all, or substantially all, of the assets of the Company (on a
         consolidated basis) to a party which is not controlled by or under
         common control with the Company, as the case may be.

                  1.1.2. "Code" means the Internal Revenue Code of 1986, as
         amended. References to a Code section shall be deemed to be to that
         section as it now exists and to any successor provision.

                  1.1.3. "Disability" means, if the Executive is covered by a
         Company sponsored disability insurance policy, total disability as
         defined in such policy without regard to any waiting period. If the
         Executive is not covered by such a policy, Disability means a physical
         or mental impairment, non-self-induced, as diagnosed by a medical
         doctor selected by the Company, that so incapacitates or disables
         Executive such that Executive is no longer able to perform the
         essential functions of his position with reasonable accommodation. As a
         condition to any benefits, the Company may require the Executive to
         submit to such physical or mental evaluations and tests as the
         Company's Board of Directors deems appropriate.

                  1.1.4. "Early Retirement Date" means the date the Executive
         attains age fifty-five (55).

                  1.1.5. "Early Retirement Percentage" means fifty percent (50%)
         on the date the Executive attains age fifty-five (55).

                  1.1.6. "Normal Retirement Date" means the date the Executive
         attains age sixty-five (65).

                  1.1.7. "Plan Year" means the twelve (12) consecutive month
         period beginning on the effective date of this Agreement and each
         anniversary thereof.

                  1.1.8. "Termination of Employment" or "Terminates Employment"
         means the Executive's ceasing to be employed by the Company for any
         reason whatsoever, voluntary or involuntary, other than by reason of an
         approved leave of absence.


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                  1.1.9. "Discount Rate" shall mean eight percent (8%).

                                   ARTICLE 2
                                LIFETIME BENEFITS

         2.1. Normal Retirement Benefit. If Termination of Executive's
Employment occurs on or after the Normal Retirement Date, the Company shall pay
to the Executive the benefit described in this Section 2.1.

                  2.1.1. Amount of Benefit. The annual benefit under this
         Section 2.1 is One Hundred Ninety-three Thousand Five Hundred Dollars
         ($193,500.00), which annual amount will be increased each Plan Year,
         until the Executive's Normal Retirement Date, by three and one-half
         percent (3.5%) compounded annually.

                  2.1.2. Payment of Benefit. The Company shall pay the annual
         benefit determined under subsection 2.1.1 for a period not to exceed
         the earlier of fifteen (15) years from Executive's Termination of
         Employment or through the month the Executive dies. The Company's
         payments shall be made in equal monthly installments (1/12 of the
         annual benefit). These equal monthly payments to the Executive will
         begin on the last day of the month which follows the month of the
         Executive's retirement and continuing until the earlier of the
         expiration of one hundred eighty (180) months from the first payment or
         the month of the Executive's death.

         2.2. Early Retirement Benefit. If Termination of Executive's Employment
occurs on or after the Early Retirement Date but before the Normal Retirement
Date, the Company shall pay to the Executive the benefit described in this
Section 2.2.

                  2.2.1. Amount of Benefit. The annual benefit under this
         Section 2.2 is One Hundred Ninety-three Thousand Five hundred Dollars
         ($193,500.00) which annual amount will be increased each Plan Year,
         until the Executive retires, by three and one-half percent (3.5%)
         compounded annually, multiplied by the Early Retirement Percentage.
         Five percent (5%) will be added to the Early Retirement Percentage for
         each anniversary of the Early Retirement Date following such date on
         which the executive continues to be employed until the Early Retirement
         Percentage equals one hundred percent (100%).

                  2.2.2. Payment of Benefit. The Company shall pay the annual
         benefit determined under subsection 2.2.1 for a period not to exceed
         the earlier of fifteen (15) years from Executive's Termination of
         Employment or through the month the Executive dies. The Company's
         payments shall be made in equal monthly installments (1/12 of the
         annual benefit). These equal monthly payments to the Executive will
         begin on the last day of the month which follows the month of the
         Executive's retirement under this Section 2.2 and continuing until the
         earlier of the expiration of one hundred eighty (180) months from the
         first payment or the month of the Executive's death.


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         2.3. Termination of Employment. If Termination of Employment occurs
before the Executive's Early Retirement Date, for reasons other than death or
Disability, the Company shall pay to the Executive the benefit described in this
Section 2.3.

                  2.3.1. Amount of Benefit. The benefit under this Section 2.3
         is the benefit set forth on the attached Schedule A based on the number
         of completed Plan Years of employment preceding the Executive's
         Termination of Employment multiplied by the vesting percentage at
         termination described in 2.3.2.

                  2.3.2. Vesting Schedule. The Executive shall vest at a rate of
         ten percent (10%) for each subsequently completed Plan Year that this
         Agreement is in force such that after ten (10) years the Executive
         shall be one hundred percent (100%) vested in the benefit.

                  2.3.3. Payment of Benefit. The Company shall pay the benefit
         in a single lump sum to the Executive within thirty (30) days following
         the Executive's Termination of Employment.

         2.4. Disability Benefit. If the Termination of Employment occurs while
the Executive suffers from a Disability prior to the Early Retirement Date, the
Company shall pay to the Executive the benefit described in this Section 2.4.

                  2.4.1. Amount and Payment of Benefit. Except as may be
         provided by Section 3.2 , the amount of benefit and method of payment
         under this Section 2.4 is established by the Executive with a written
         election and filed with the Company. The Company shall pay the elected
         amount to the Executive in accordance with the written election made by
         the Executive. The form of the election shall follow the form and
         content found on the attached Exhibit A. The attached Exhibit A,
         including the terms governing the Executive's election under this
         Section 2.4.1, are incorporated into this Agreement by reference.

         2.5. Change of Control Benefit. Upon a Change of Control while the
Executive is in the active service of the Company and (i) the Company thereafter
terminates the Executive; or (ii) the Executive terminates his employment after
either a change in job responsibilities or a reduction in the compensation paid
annually to the Executive prior to his Normal Retirement Date, then the Company
shall pay to the Executive the benefit described in this Section 2.5 in lieu of
any other benefit under this Agreement.

                  2.5.1. Amount and Payment of Benefit. The benefit under this
         Section 2.5 is one hundred percent (100%) of the benefit determined
         under Schedule A based on the number of completed Plan Years, in
         accordance with Schedule A, on the date of Termination of Employment.
         The Company shall pay this benefit to the Executive in a single lump
         sum within thirty (30) days from Termination of Employment following a
         Change in Control.


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                  2.5.2. Parachute Payment. If it is determined that any portion
         of the benefit payment to the Executive under this Agreement
         constitutes a parachute payment under Section 280G of the Code subject
         to the excise tax of Section 4999 of the Code, the Executive shall be
         entitled to receive from the Company a lump sum cash payment sufficient
         to place the Executive in the same net after tax position that the
         Executive would have been in had such payment not been subject to such
         excise tax; provided, however, the Executive shall be entitled to a
         payment under this Section 2.5.2 only to the extent that the Executive
         is not entitled to an equivalent payment under any other agreement.

         2.6. Payment of Benefits in Pay Status. Upon a Change of Control where
benefits are in pay status to the Executive following the Executive's
retirement, death, or Disability, one hundred percent (100%) of the present
value of any remaining payments otherwise due pursuant to this Agreement will,
in lieu of such remaining payments, be paid in full in a lump sum within thirty
(30) days after a Change in Control. The Discount Rate shall be used to
determine present value.

                                   ARTICLE 3
                                 DEATH BENEFITS

         3.1 Death During Active Service. If the Executive dies while employed
by the Company and prior to receiving any payments under this Agreement, the
Company shall have no obligation to pay to the Executive's beneficiary any
amount under this Agreement.

         3.2 Death Subsequent to Either Retirement Date. If the Executive dies
subsequent to the date that he retires and while receiving payments under
Section 2.1 or Section 2.2 of this Agreement, the Company's obligation to make
the final payment under Section 2.1.2 or Section 2.2.2 on the last day of the
month of the Executive's death shall constitute the Company's final obligation
to pay the Executive or the Executive's estate under the terms of this
Agreement.

         3.3 Death During Disability. In the event of the Executive's death
following Termination of Employment while suffering a Disability, but where the
termination is prior to Early Retirement Age, the Company shall have no
obligation to pay to the Executive's beneficiary any amount under this
Agreement.

                                   ARTICLE 4
                               GENERAL LIMITATIONS

         Notwithstanding any provision of this Agreement to the contrary, the
  Company shall not pay any benefit under this Agreement:

         4.1. Termination for Cause. If the Company terminates the Executive's
employment for any of the following reasons:

                  4.1.1. Gross negligence or gross neglect of duties;


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                  4.1.2. Commission of a felony or of a misdemeanor involving
         moral turpitude; or

                  4.1.3. Fraud, dishonesty or willful violation of any law or
         significant Company policy committed in connection with the Executive's
         employment and resulting in personal financial benefit to the Executive
         and in an adverse effect on the Company.

                                   ARTICLE 5
                          CLAIMS AND REVIEW PROCEDURES

         5.1. Claims Procedure. The Company shall notify the Executive in
writing, within ninety (90) days of his written application for benefits, of his
eligibility or ineligibility for benefits under the Agreement. If the Company
determines that the Executive is not eligible for benefits or full benefits, the
notice shall set forth (1) the specific reasons for such denial, (2) a specific
reference to the provisions of the Agreement on which the denial is based, (3) a
description of any additional information or material necessary for the claimant
to perfect his or her claim, and a description of why it is needed, and (4) an
explanation of the Agreement's claims review procedure and other appropriate
information as to the steps to be taken if the beneficiary wishes to have the
claim reviewed. If the Company determines that there are special circumstances
requiring additional time to make a decision, the Company shall notify the
Executive of the special circumstances and the date by which a decision is
expected to be made, and may extend the time for up to an additional ninety-day
period.

         5.2. Review Procedure. If the Executive is determined by the Company
not to be eligible for benefits, or if the Executive believes that he is
entitled to greater or different benefits, the Executive shall have the
opportunity to have such claim reviewed by the Company by filing a petition for
review with the Company within sixty (60) days after receipt of the notice
issued by the Company. Said petition shall state the specific reasons which the
Executive believes entitle him to benefits or to greater or different benefits.
Within sixty (60) days after receipt by the Company of the petition, the Company
shall afford the Executive (and counsel, if any) an opportunity to present his
position to the Company orally or in writing, and the Executive (or counsel)
shall have the right to review the pertinent documents. The Company shall notify
the Executive of its decision in writing within the sixty-day period, stating
specifically the basis of its decision, written in a manner calculated to be
understood by the Executive and the specific provisions of the Agreement on
which the decision is based. If, because of the need for a hearing, the
sixty-day period is not sufficient, the decision may be deferred for up to
another sixty-day period at the election of the Company, but notice of this
deferral shall be given to the Executive.

                                   ARTICLE 6
                           AMENDMENTS AND TERMINATION

         6.1. Amendment or Termination of Agreement After a Change in Control.
The Company may amend or terminate this Agreement at any time prior to the
Executive's Termination of Employment by written notice to the Executive;
provided, however, that if the Company amends or terminates this Agreement prior
to the Executive's Normal Retirement Date while the Executive is in the active
service of the Company and subsequent to a Change of


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Control, then the Company shall pay the Executive one hundred percent (100%) of
the benefit determined under Schedule A based on the number of completed Plan
Years, in accordance with Schedule A, on the date of termination of this
Agreement. The Company shall pay this benefit to the Executive in a single lump
sum within thirty (30) days from Termination of Agreement following a Change in
Control.

         6.2. Amendment or Termination Prior to a Change in Control. The Company
may amend or terminate this Agreement at any time prior to a Change in Control
by written notice to the Executive.

                  6.2.1. Subsequent to Executive's Normal Retirement Date. In
         the event of any such amendment or termination after payment of
         benefits has commenced, the benefit the Executive shall be entitled is
         one hundred percent (100%) of the present value of any unpaid benefit
         under Article 2. The Discount Rate shall be used to determine present
         value. The Company shall pay the benefit under this Section 6.2.1 in a
         single lump sum payment within sixty (60) days of amendment or
         termination of this Agreement.

                  6.2.2. Prior to Executive's Normal Retirement Date. If
         amendment or termination of this Agreement under Section 6.2 occurs
         after the effective date of this Agreement and before payment of
         benefits has commenced, the Company shall pay the Executive an amount
         equal to one hundred percent (100%) of the amount of accrued benefit
         reflected in Schedule A based o completed Plan Years. The Company shall
         pay this benefit, if any, to the Executive in a single lump sum payment
         within sixty (60) days of Agreement amendment or termination.

                                   ARTICLE 7
                                  MISCELLANEOUS

         7.1. Binding Effect. This Agreement shall bind the Executive and the
Company, and their beneficiaries, survivors, executors, administrators and
permitted transferees.

         7.2. No Guaranty of Employment. This Agreement is not an employment
policy or contract. It does not give the Executive the right to remain an
employee of the Company, nor does it interfere with the Company's right to
discharge the Executive. It also does not require the Executive to remain an
employee nor interfere with the Executive's right to terminate employment at any
time.

         7.3. Non-Transferability. Benefits under this Agreement cannot be sold,
transferred, assigned, pledged, attached or encumbered in any manner.

         7.4. Tax Withholding. The Company shall withhold any taxes that are
required to be withheld from the benefits provided under this Agreement.


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         7.5. Applicable Law. The Agreement and all rights hereunder shall be
governed by the laws of the State of Missouri, except to the extent preempted by
the laws of the United States of America.

         7.6. Unfunded Arrangement. The Executive is a general unsecured
creditor of the Company for the payment of benefits under this Agreement. The
benefits represent the mere promise by the Company to pay such benefits. The
rights to benefits are not subject in any manner to anticipation, alienation,
sale, transfer, assignment, pledge, encumbrance, attachment, or garnishment by
creditors. Any insurance on the Executive's life is a general asset of the
Company to which the Executive has no preferred or secured claim.

         7.7. Severability. Without limitation of any other section contained
herein, in case any one or more provisions contained in this Agreement shall for
any reason be held to be invalid, illegal or unenforceable in any other respect,
such invalidity, illegality or unenforceability shall not affect the other
provisions of this Agreement. This Agreement shall be construed as if such
invalid, illegal or unenforceable provision had never been a part of this
Agreement and shall be deemed substituted therefore such other provisions as
will most nearly accomplish the intent of the parties to the extent permitted by
applicable law, in case this Agreement or any one or more of its provisions
shall be held to be invalid, illegal or unenforceable by any governmental
regulatory agency or court of competent jurisdiction.


         IN WITNESS WHEREOF, the Executive and a duly authorized Company officer
have signed this Agreement as of the date indicated below.



    /s/ Thomas M. Teschner                              Date: 12/1/99
THOMAS M. TESCHNER

SOUTHSIDE BANCSHARES CORP.



By:  /s/ Joseph W. Pope                                 Date: 12/1/99
Title:  Chief Financial Officer


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                                    EXHIBIT A

                      EXECUTIVE RETIREMENT BENEFIT ELECTION

         THIS ELECTION is made and entered into as of 1st day of December, 1999,
by SOUTHSIDE BANCSHARES CORP. (the "Company") located in St. Louis, Missouri,
pursuant to the Salary Continuation Agreement between the Company and THOMAS M.
TESCHNER (the "Executive") dated December 1, 1999, (the "Agreement").

         The Executive, by initialing in ink either OPTION 1 or OPTION 2 below
hereby elects to receive the Disability Benefit described in the elected option
and receive the payment or payments in accordance to the option the Executive
elects.


                                    OPTION 1

                  (initials)
         ---------

                  a. Benefit Amount. The amount of the benefit is the amount set
         forth on the attached Schedule A based on the number of completed Plan
         Years preceding the Executive's Termination of Employment.

                  b. Payment of Benefit. The Company shall pay the benefit in a
         single lump sum to the Executive within thirty (30) days following the
         Executive's Termination of Employment.

                                    OPTION 2

          /s/TMT  (initials)
         ---------

                  a. Benefit Amount. The amount of the benefit is a percentage
         of the annual benefit set forth in Section 2.1 determined as of the
         Normal Retirement Date. The fraction to be utilized to determine the
         percentage has a numerator equal to the amount found on Schedule A of
         the Agreement based upon the number of completed Plan Years by the
         Executive as of Termination of Employment increased each subsequent
         Plan Year until the Executive's Normal Retirement Date by six percent
         (6%) and a denominator equal to the amount found on Schedule A of the
         Agreement based upon the Executive having completed all Plan Years up
         to the Executive's Normal Retirement Date. The Discount Rate as
         described in Section 1.1.9 of the Agreement shall be used to determine
         the present value.

                  b. Payment of Benefit. The Company shall pay the annual
         benefits for a period of fifteen (15) years from Executive's Normal
         Retirement Date. The Company's payments shall be made in equal monthly
         installments (1/12th of the annual benefit). These equal monthly
         payments to the Executive will begin on the last day of the month which
         follows the month of the Executive attaining the Normal Retirement Date
         and continuing until the expiration of one hundred eighty (180) months
         from the first payment.


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                              EXHIBIT A (CONTINUED)

         The Executive and Company acknowledge and agree that each and every
election to select a benefit payment pursuant to OPTION 1 or OPTION 2 made under
this EXHIBIT A EXECUTIVE RETIREMENT BENEFIT ELECTION, in order to be valid and
effective, must be made by December 31st of the year prior to the calendar year
preceding the Executive's Termination of Employment.

         The Executive and Company agree and acknowledge that any election to
select a benefit payment pursuant to OPTION 1 or OPTION 2 made under this
EXHIBIT A EXECUTIVE RETIREMENT BENEFIT ELECTION not made within the time frame
set forth in the paragraph above shall be null and void. When a null and void
election is made the most recent election which is not null and void shall
determine the method in which the Executive's retirement benefit shall be paid
under Section 2.4.1 of the Agreement.

         The Executive and the Company acknowledge and agree that the Company,
in the absence of a valid election by the Executive under this EXHIBIT A
EXECUTIVE RETIREMENT BENEFIT ELECTION, the Company shall pay any benefit under
Section 2.4.1 of this Agreement under OPTION 1 above.

         The Executive and the Company understands that the Executive may change
the election set forth above, consistent with the restrictions set forth in this
EXHIBIT A EXECUTIVE RETIREMENT BENEFIT ELECTION, by filing a new written
designation with the Company on a form following this EXHIBIT A EXECUTIVE
RETIREMENT BENEFIT ELECTION.

Executive:

Signature    /s/ Thomas M. Teschner          Date        December 1, 1999
            --------------------------       -----------------------------


Accepted by the Company this 1st day of December, 1999.

By:   /s/ Joseph W. Pope
Title: Chief Financial Officer


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                                   SCHEDULE A

                      SALARY CONTINUATION AGREEMENT BETWEEN
                 SOUTHSIDE BANCSHARES CORP. AND THOMAS TESCHNER


<TABLE>
<CAPTION>
          Plan Year* Completed
       before Termination occurs                   Compensation Balance
       -------------------------                   --------------------
<S>                                                <C>
                  1                                      $ 29,307
                  2                                        62,178
                  3                                        99,068
                  4                                       140,500
                  5                                       187,069
                  6                                       239,456
                  7                                       298,447
                  8                                       364,947
                  9                                       440,002
                  10                                      524,835
                  11                                      620,875
                  12                                      729,812
                  13                                      853,658
                  14                                      994,840
                  15                                    1,156,330
                  16                                    1,341,839
                  17                                    1,556,131
                  18                                    1,805,560
                  19                                    2,099,108
                  20                                    2,450,713
                  21                                    2,886,007
                  22                                    3,474,940

            End of Schedule
</TABLE>
<PAGE>   13
                             SCHEDULE A (CONTINUED)

                      SALARY CONTINUATION AGREEMENT BETWEEN
                 SOUTHSIDE BANCSHARES CORP. AND THOMAS TESCHNER


     * Plan Year means the anniversary year of the date of the Agreement.

     To calculate an amount for less than a full Plan Year, take the number of
     completed months of service into the current Plan Year and divide by 12.
     Then multiply that fraction by the difference between (i) the Plan Year
     balance shown above for the Plan Year in which termination occurs and (ii)
     the previous Plan Year's balance. Then add that amount to the previous Plan
     Year's balance. The result provides credit for all prior full plan years
     plus a ratio percentage of the current plan year. For example, if the
     Executive leaves the Bank during the 5th plan year four months after the
     fourth year plan anniversary, then you would take 4/12 times the balance
     shown for Plan Year 5 minus the balance shown for Plan Year 4. Then add
     that amount to the balance shown for Plan Year 4 to determine the amount
     due as a termination payment.


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