<PAGE>
                                                                   EXHIBIT 10.11



                            PRODUCT SUPPLY AGREEMENT

This agreement is entered into on this ____ day of ____ 2002, between Martin Gas
Sales, Inc. (hereinafter referred to as "Seller") with corporate office located
at 4200 Stone Road, Kilgore, TX 75662 and Martin Midstream Partners L.P.
(hereinafter referred to as "Buyer") with corporate office located at 4200 Stone
Road, Kilgore, TX 75662.

     1.   DEFINITIONS

          1.1  "Product" shall mean 93% or 98% sulfuric acid as shown in Exhibit
               A.

     2.   AGREEMENT TERM

          2.1  The term (hereinafter referred to as the "Initial Term") of this
               Agreement shall be three (3) years beginning on July 1, 2002.
               After the Initial Term, the term shall automatically renew from
               year to year, unless either party gives written notice at least
               thirty (30) days prior to the expiration of the Initial Term or
               of any renewal term. If any Product deliveries are made before
               the indicated beginning date, that Product will also be covered
               by this Agreement.

     3.   QUANTITY

          3.1  Seller agrees to supply and Buyer agrees to purchase from Seller,
               100% of Buyer's Plainview, Texas plant requirements, currently
               estimated at 8,000 tons per month. Seller also recognizes that
               Buyer may choose not to run the Plainview, Texas plant based on
               market conditions and Seller will adjust supply depending on
               Buyer's needs.

     4.   PRICING

          4.1  Seller agrees to supply Buyer with Product at a price equal to
               Seller's best available cost plus $4/short ton.

          4.2  Additionally, if Seller requires truck tons F.O.B. Buyer's plant,
               Buyer agrees to provide tons to Seller at Buyer's cost plus
               $4/ton.

     5.   PAYMENT TERMS

          5.1  All invoices will be paid net thirty (30) days from shipment by
               Seller.

     6.   SEVERABILITY

          6.1  If any provision of this Agreement is found to be illegal or
               unenforceable, Such provision shall be deemed not to part of this
               Agreement and this Agreement shall continue in full force and
               effect, but shall be interpreted


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               to give effect to the extent feasible to the original written
               intent of the parties.

     7.   ENTIRE AGREEMENT

          7.1  This Agreement sets forth the entire Agreement between Seller and
               Buyer with respect to Product. This Agreement supercedes and
               cancels all prior and contemporaneous agreements and
               understanding between the parties, whether oral or written,
               relating to this product. Exhibit A attached hereto is made a
               part hereof and are incorporated herein by reference.

     8.   CONTROLLING LAW

          8.1  This Agreement shall be governed by and construed in accordance
               with the laws of the State of Texas.

          IN WITNESS WHEREOF the duly authorized parties hereto as of the date
first set forth above have duly executed this Agreement.


MARTIN GAS SALES, INC.

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



MARTIN MIDSTREAM PARTNERS L.P.

By:  Martin Midstream GP LLC


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

<PAGE>


                                   EXHIBIT "A"



                             MARTIN GAS SALES, INC.
                 93% AND 98% GRADE SULFURIC ACID SPECIFICATIONS


<Table>
<Caption>
                                         Typical            Guaranteed Maximum
               Element                   Analysis                  98%
               -------                   --------           ------------------

<S>                                       <C>                <C>
                H2S04                     98.5%               97.8 - 99.5%

                H2S04                     93.5%               92.8 - 94.2%

              Iron (Fe)                   15 ppm                 50 ppm

        Sulphur Dioxide (SO2)            <25 ppm                 50 ppm

              Nitrates                     5 ppm                <50 ppm

            Heavy Metals                  <5 ppm                 20 ppm
</Table>