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                                                                   EXHIBIT 10.4a

                                 FIRST AMENDMENT
                                     TO THE
                            STERLING CHEMICALS, INC.
              AMENDED AND RESTATED SALARIED EMPLOYEES' PENSION PLAN

                  WHEREAS, there is reserved to Sterling Chemicals, Inc.
("Chemicals") in Section 15.1 of the Sterling Chemicals, Inc. Amended and
Restated Salaried Employees' Pension Plan (the "Plan") the right to amend the
Plan; and

                  WHEREAS, Sterling Fibers, Inc. ("Fibers"), a subsidiary of
Chemicals, has adopted the Plan for its eligible employees in conjunction with
the purchase of certain operations from Cytec Industries, Inc. and its
affiliates ("Cytec");

                  NOW, THEREFORE, the Plan is hereby amended effective as of
January 31, 1997 by adding thereto the following:

                  1. Each Cytec employee who became an employee of Fibers on
         January 31, 1997 shall receive credit for his service that was credited
         under the Cytec Salaried and Nonbargaining Employees' Retirement Plan
         ("Cytec Plan") on January 31, 1997 for eligibility and vesting purposes
         only under the Plan.

                  2. Each such former Cytec employee who retires under the Plan
         during the period beginning February 1, 1997 and ending January 31,
         1999, shall receive a supplemental monthly straight life annuity
         benefit equal to the excess of (1) the monthly straight life annuity
         benefit he would have received under the Cytec Plan, had he remained
         employed with Cytec from February 1, 1997 through his retirement date
         under the Plan, and (2) the monthly straight life annuity benefit he
         would be entitled to receive under the Plan but for this paragraph 2
         ("basic benefit"). Notwithstanding the foregoing however, if the
         Participant receives his basic benefit in a form other than a straight
         life annuity, the supplemental benefit provided by this paragraph 2
         shall be paid in the same form as is his basic benefit and shall be
         actuarially adjusted in the same manner as is his basic benefit.

                  All terms used herein that are defined in the Plan shall have
the same meanings given to such terms in the Plan, except as otherwise expressly
provided herein.

                  Except as amended and modified hereby, the Plan shall continue
in full force and effect and the Plan and this amendment shall be read, taken
and construed as one and the see instrument.

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                  This amendment may be executed in several counterparts, each
of which shall be deemed an original, but all of which shall constitute but one
and the same instrument which may be evidenced by any one counterpart.

                  IN WITNESS WHEREOF, Chemicals has executed this instrument
effective for all purposes as of the date provided above.

                                          STERLING CHEMICALS, INC.

                                          By:
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                                                                   EXHIBIT 10.4b

                                SECOND AMENDMENT
                                     TO THE
                            STERLING CHEMICALS, INC.
              AMENDED AND RESTATED SALARIED EMPLOYEES' PENSION PLAN

                  WHEREAS, there is reserved to Sterling Chemicals, Inc.
("Chemicals") in Section 15.1 of the Sterling Chemicals, Inc. Amended and
Restated Salaried Employees' Pension Plan (the "Plan") the right to amend the
Plan;

                  NOW, THEREFORE, the Plan is hereby amended by adding thereto a
new Section 9.10A to read as follows:

                  9.10A Canadian Employees Transferred to Salaried Basis. The
         Monthly Retirement Income payable to a participant, who was an employee
         of a Canadian Affiliate Company prior to the date his participation
         under this Plan commenced and who is otherwise entitled to a benefit
         under a defined benefit pension plan maintained by the Canadian
         Affiliate Company (the "Canadian Plan"), with respect to his
         participation in this Plan and his participation in the Canadian Plan
         shall be the greater of:

                  (a) the Monthly Retirement Income or Monthly Vested
         Termination Benefit computed under this Plan as if all benefit service
         accrued under the Canadian Plan and this Plan had been accrued under
         this Plan alone; or

                  (b) the sum of:

                           (i) the Monthly Retirement Income or Monthly Vested
                  Termination Benefit under this Plan computed on the basis of
                  his benefit service solely attributable to his service with
                  the Employers on and after the date his participation in this
                  Plan commenced; and

                           (ii) his non-contributory regular benefits under the
                  Canadian Plan determined on the basis of his benefit service
                  accrued under the Canadian Plan prior to the date his
                  participation in this Plan commenced. Such regular benefits
                  shall be computed on the basis of the provisions of the
                  Canadian Plan as in effect on the date he ceased to be an
                  employee of the Canadian Affiliate Company.

                           There shall be no duplication of benefits for the
         same period of time and if paragraph (a) above is applicable, the
         benefits payable hereunder shall be reduced by the actuarial
         equivalence of the benefits payable under the Canadian Plan. A
         participant subject to this Section 9.10A must retire under both the
         Canadian Plan and this Plan at the same time.

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                  All terms used herein that are defined in the Plan shall have
the same meanings given to such terms in the Plan, except as otherwise expressly
provided herein.

                  Except as amended and modified hereby, the Plan shall continue
in full force and effect and the Plan and this amendment shall be read, taken
and construed as one and the same instrument.

                  This amendment may be executed in several counterparts, each
of which shall be deemed an original, but all of which shall constitute but one
and the same instrument which may be evidenced by any one counterpart.

                  IN WITNESS WHEREOF, Chemicals has executed this instrument to
be effective as of January 1, 1997 upon the receipt of a favorable IRS
determination letter for this amendment.

                                               STERLING CHEMICALS, INC.

                                               By:
                                                   -----------------------------<PAGE>   1
                                                                   EXHIBIT 10.4c

                                 THIRD AMENDMENT
                                     TO THE
                            STERLING CHEMICALS, INC.
              AMENDED AND RESTATED SALARIED EMPLOYEES' PENSION PLAN

                  WHEREAS, there is reserved to Sterling Chemicals, Inc. (the
"Company") in Section 15.1 of the Sterling Chemicals, Inc. Amended and Restated
Salaried Employees' Pension Plan (the "Plan") the right to amend the Plan;

                  NOW, THEREFORE, the Plan is hereby amended effective as of
November 1, 1998, as follows:

         1.       Section 3.2 is amended to read as follows:

                  "Early Retirement Date. A participant's "Early Retirement
                  Date" will be the first day of the month following the month
                  in which he retires from the employ of all the Employers
                  before his Normal Retirement Date, but after he has both
                  attained at least age 55 years and is vested pursuant to
                  Section 2.2. However, a participant who receives Post Benefit
                  Service credit pursuant to Section 17.4(a)(vii) will, upon
                  reaching age 55, be deemed to have terminated his employment
                  on having reached such date."

         2.       A new subparagraph (vii) is added to Section 17.4(a) to read
                  as follows:

                  If a participant between the ages of 54 and 55 is
                  involuntarily terminated by an Employer other than for cause
                  as part of a formal reduction in force or layoff program, the
                  participant will continue to receive Post Benefit Service
                  credit until he attains the age of 55; provided, however,
                  there shall be no duplication of Post Benefit Service that is
                  credited for the same period of time under any other provision
                  of the Plan.

                  All terms used herein that are defined in the Plan shall have
the same meanings given to such terms in the Plan, except as otherwise expressly
provided herein.

                  Except as amended and modified hereby, the Plan shall continue
in full force and effect and the Plan and this amendment shall be read, taken
and construed as one and the same instrument.

                  This amendment may be executed in several counterparts, each
of which shall be deemed an original, but all of which shall constitute but one
and the same instrument which may be evidenced by any one counterpart.

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                  IN WITNESS WHEREOF, the Company has executed this instrument
this _______________, 1999, effective for all purposes as provided above.

                                         STERLING CHEMICALS, INC.

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

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