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                                                                EXHIBIT 10.26(a)

                   FIRST AMENDMENT TO JOINT VENTURE AGREEMENT


         THIS AMENDMENT is entered into and effective as of the 31st day of
March, 1998, by and between BP CHEMICALS INC. ("BP") and STERLING CHEMICALS,
INC. ("Sterling").

         WHEREAS, BP and Sterling are parties to a certain Joint Venture
Agreement executed and effective as of March 31, 1998 ("Agreement"); and

         WHEREAS, BP and Sterling wish to modify the Agreement as hereinafter
set forth;

         NOW, THEREFORE, in consideration of the mutual covenants and agreements
herein contained, and intending to be legally bound, BP and Sterling hereby
amend the Agreement in the following respects:

         1.     Section 3.4.3 of the Agreement is hereby amended to read in its
entirety as follows:

                "3.4.3   The Parties shall *****

         2.     Section 3.6 of the Agreement is hereby amended to read in its
entirety as follows:

                "3.6     Price and Terms.  The Company shall *****

         3.     The seventh sentence of Section 5.1 of the Agreement is hereby
amended to read in its entirety as follows: *****

         4.     Section 5.6 of the Agreement is hereby amended to read in its
entirety as follows:

                "5.6 Volume Imbalances. Company purchases of Acrylonitrile
                loaded for shipment during each calendar quarter shall be
                provisionally allocated between the



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                Parties based, as nearly as possible, on each Party's then
                applicable BRV Ratio. At the end of each calendar year, each
                Party's actual BRV for that calendar year shall be reconciled
                with its provisionally allocated volume during that year and any
                difference or imbalance shall be added to the underallocated
                Party's BRV and subtracted from the overallocated Party's BRV
                for the next calendar year, as described in attached Exhibit D,
                to determine purchases by the Company from the Parties in such
                calendar year; provided, however, that such reconciliation of
                any volume imbalances shall not affect the Parties' respective
                BRVs or BRV Ratios for any other purpose under this Agreement."

         5.     Exhibit D of the Agreement is hereby replaced in its entirety by
the attached Exhibit D.

         6.     The sentence  *****

         7.     To the extent that the terms of this Amendment vary from the
terms of the Agreement, this Amendment shall constitute an amendment of the
Agreement. Except as amended and modified by this Amendment, the Agreement shall
continue in full force and effect. The Agreement and this Amendment shall be
read, taken and construed as one and the same instrument. Upon the effectiveness
of this Amendment, each reference in the Agreement to "this Agreement" shall
mean and be a reference to the Agreement as amended hereby.

         8.     This Amendment shall not be or become effective unless and until
it has been duly executed and delivered by the parties but, upon such execution
and delivery, shall be effective as of March 31, 1998.

         9.     This Amendment shall inure to the benefit of, and shall be
binding upon the parties and their respective successors and permitted assigns.

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         10.    This Amendment may be executed in two or more counterparts, each
of which shall be deemed an original but all of which taken together shall
constitute one and the same agreement. It shall not be necessary in making proof
of this Amendment to produce or account for more than one such counterpart.

         11.    Should any clause, sentence, paragraph, subsection or Section of
this Amendment be judicially declared to be invalid, unenforceable or void, such
decision will not have the effect of invalidating or voiding the remainder of
this Amendment, and the parties agree that the part or parts of this Amendment
so held to be invalid, unenforceable or void will be deemed to have been
stricken herefrom as if such stricken part or parts had never been included
herein.

         12.    THIS AMENDMENT SHALL BE CONSTRUED AND ENFORCED IN ACCORDANCE
WITH, AND THE RIGHTS OF THE PARTIES SHALL BE GOVERNED BY, THE INTERNAL LAWS OF
THE STATE OF DELAWARE, WITHOUT REFERENCE TO PRINCIPLES OF CONFLICTS OF LAW.

         13.    This Amendment and the Agreement set forth all of the promises,
agreements, conditions, understandings, warranties and representations between
the parties with respect to the matters cover hereby, and supersede all prior
agreements, arrangements and understandings between the parties, whether
written, oral or otherwise. There are no promises, agreements, conditions,
understandings, warranties or representations, oral or written, express or
implied, between the parties concerning the subject matter hereof or thereof
except as set forth herein or therein.

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         IN WITNESS WHEREOF, the parties hereto have caused this Amendment to be
executed by their duly authorized representatives as of the date first written
above.

BP CHEMICALS INC.                      STERLING CHEMICALS, INC.

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



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                                    EXHIBIT D

                         PRICE AND VOLUME RECONCILIATION


                                      *****



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