<PAGE>
                                                                    EXHIBIT 10.1

                           AMENDMENT TO LOAN AGREEMENT
                            AND MODIFICATION OF NOTE

     THIS AMENDMENT TO LOAN AGREEMENT ("Amendment") dated as of June 21, 2002
(the "Amendment Effective Date"), is made and entered into by and between EVANS
SYSTEMS, INC., a Texas corporation (the "Borrower"), and CAIN, SMITH & STRONG,
L.P, a Delaware limited partnership ("Lender") and successor-in-interest to
CHASE BANK OF TEXAS, NATIONAL ASSOCIATION.

                                    RECITALS:

     WHEREAS, the Borrower and the Lender are parties to a Loan Agreement dated
as of August 30, 1996, as heretofore amended (the "Loan Agreement"); and

     WHEREAS, the Borrower executed and delivered to the Lender (i) that certain
promissory note dated August 4, 1997 in the original principal amount of
$8,700,000, and (ii) that certain promissory note dated January 26, 2000 in the
original amount of $1,000,000 (collectively, the "Notes"); and

     WHEREAS, the Borrower and the Lender have agreed, on the terms and
conditions herein set forth, that the Loan Agreement and the Notes be amended in
certain respects;

     NOW THEREFORE, FOR GOOD AND VALUABLE CONSIDERATION, THE RECEIPT AND
SUFFICIENCY OF WHICH IS HEREBY ACKNOWLEDGED, IT IS AGREED:

     SECTION 1. Definitions. Terms used herein that are defined in the Loan
Agreement shall have the same meanings when used herein unless otherwise
provided herein.

     SECTION 2. Amendments to the Loan Agreement. From and after the Amendment
Effective Date:

     (a) New Paragraph 2(e) of the Loan Agreement is hereby added, which shall
read in its entirety as follows:

          (e) Upon execution of this Agreement and in consideration for Lender's
     agreement to discount the outstanding indebtedness of Borrower under this
     Loan Agreement by $700,000.00 and other consideration contained in this
     agreement, Borrower hereby agrees to convey to Lender the real property
     described on Exhibit "A" attached hereto, together with all buildings,
     fixtures and other improvements located thereon and all rights, easements,
     hereditaments and appurtenances related thereto. Notwithstanding the
     foregoing, Lender hereby agrees that in lieu of contributing said real
     property to the wholly owned limited partnerships set forth on Exhibit "A",
     the same shall be conveyed by Borrower directly to such limited
     partnerships.
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     (b) New Paragraph 2(f) of the Loan Agreement is hereby added, which shall
read in its entirety as follows:

          (f) Upon execution of this Agreement and in consideration for Lender's
     extinguishment of the outstanding unsecured indebtedness of Borrower
     described on Schedule "A" attached hereto and other consideration contained
     in this agreement, Borrower hereby agrees to convey to Lender the real
     property described on Exhibit "A" attached hereto, together with all
     buildings, fixtures and other improvements located thereon and all rights,
     easements, hereditaments and appurtenances related thereto. Notwithstanding
     the foregoing, Lender hereby agrees that in lieu of contributing said real
     property to the wholly owned limited partnerships set forth on Exhibit "A",
     the same shall be conveyed by Borrower directly to such limited
     partnerships.

     (c) New Paragraph 2(g) of the Loan Agreement is hereby added, which shall
read in its entirety as follows:

          (g) Upon execution of this Agreement and in consideration for Lender's
     extinguishment of the outstanding trust accounts of Borrower described on
     Schedule "B" attached hereto, Borrower hereby agrees to convey to Lender
     the real property described on Exhibit "A" attached hereto, together with
     all buildings, fixtures and other improvements located thereon and all
     rights, easements, hereditaments and appurtenances related thereto.
     Notwithstanding the foregoing, Lender hereby agrees that in lieu of
     contributing said real property to the wholly owned limited partnerships
     set forth on Exhibit "A", the same shall be conveyed by Borrower directly
     to such limited partnerships.

     (d) The real property conveyances described in paragraphs (a), (b) and (c)
of this Section 2 shall be effected pursuant to the seven General Warranty Deeds
attached hereto as Exhibit "D". In addition, Borrower shall deliver to Lender
Environmental Indemnity Agreements for each of the parcels of real property
described in the Exhibits to this Section 2, which shall be in the form of
Exhibit "E" attached hereto.

     SECTION 3. Modification of Notes. On and after the Amendment Effective
Date:

     (a) The Notes are hereby modified by (i) reducing the aggregate outstanding
principal balance of the Notes as of the Amendment Effective Date from
$5,200,000.00 to $4,500,000.00, (ii) deferral of the principal payments under
the Notes until July 1, 2007, which shall be the new Stated Maturity Date of the
Notes, as such term is defined under the Loan Agreement, (iii) changing the
interest rate (defined as Base Rate in the Loan Agreement) on the Notes to 10%,
and (iv) deferral of interest payments under the Notes for a period of six moths
from the Amendment Effective Date, with interest only thereafter for a period of
54 months. The entire unpaid principal balance together with accrued interest
shall be due and payable on the Stated Maturity Date, if not paid sooner.

     SECTION 4. Release of Guarantor. In consideration for the agreement by J.
L.Evans, Sr. ("Evans") to convey to JPMorganChase of 1,104,015 shares of common
stock of the

                                       2
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Company beneficially owned by Evans, Lender hereby releases Evans from that
certain Guaranty dated January 26, 2000, and all obligations and liabilities
arising thereunder.

     SECTION 5. Additional Security Interest. In order to secure the prompt and
unconditional payment of the indebtedness under the Loan Agreement and the Notes
and in consideration for Lender's agreement to enter into this Amendment,
Borrower hereby agrees to grant Lender a security interest in all of Borrower's
property, to the extent not already encumbered by Lender, whether now existing
or hereafter acquired, created or arising. Borrower hereby agrees to provide
Lender with such assistance as may be reasonably requested in connection with
carrying into effect the rights granted pursuant to this Section 5.

     SECTION 6. Limitations. The amendments set forth herein are limited
precisely as written and shall not be deemed to (a) be a consent to, or waiver
or modification of, any other term or condition of the Loan Agreement or any of
the other Credit Documents, or (b) except as expressly set forth herein,
prejudice any right or rights which the Lender may now have or may have in the
future under or in connection with the Loan Agreement, the Credit Documents or
any of the other documents referred to therein. Except as expressly modified
hereby or by express written amendments thereof, the terms and provisions of the
Loan Agreement, the Notes, and any other Credit Documents or any other documents
or instruments executed in connection with any of the foregoing are and shall
remain in full force and effect. In the event of a conflict between this
Amendment and any of the foregoing documents, the terms of this Amendment shall
be controlling. The representations and warranties made in that certain Common
Stock Purchase agreement between Borrower and Mauritz & Couey of even date
herewith are true and correct in all respects on and as of the Amendment
Effective Date.

     SECTION 7. Payment of Expenses. The Borrower agrees, whether or not the
transactions hereby contemplated shall be consummated, to reimburse and save the
Lender harmless from and against liability for the payment of all reasonable
substantiated out-of-pocket costs and expenses arising in connection with the
preparation, execution, delivery, amendment, modification, waiver and
enforcement of, or the preservation of any rights under this Amendment,
including, without limitation, the reasonable fees and expenses of any local or
other counsel for the Lender, and all stamp taxes (including interest and
penalties, if any), recording taxes and fees, filing taxes and fees, and other
charges which may be payable in respect of, or in respect of any modification
of, the Loan Agreement and the Other Credit Documents. The provisions of this
Section shall survive the termination of the Loan Agreement and the repayment of
the Loans.

     SECTION 8. Governing Law. This Amendment and the rights and obligations of
the parties hereunder and under the Loan Agreement shall be construed in
accordance with and be governed by the laws of the State of Texas and the United
States of America.

     SECTION 9. Descriptive Headings, Etc. The descriptive headings of the
several Sections of this Amendment are inserted for convenience only and shall
not be deemed to affect the meaning or construction of any of the provisions
hereof.

     SECTION 10. Entire Agreement. This Amendment and the documents referred to
herein represent the entire understanding of the parties hereto regarding the
subject matter

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<PAGE>

hereof and superseded all prior and contemporaneous oral and written agreements
of the parties hereto with respect to the subject matter hereof, including,
without limitation, any commitment letters regarding the transactions
contemplated by this Amendment.

     SECTION 11. Counterparts. This Amendment may be executed in any number of
counterparts and by different parties on separate counterparts and all of such
counterparts shall together constitute one and the same instrument.

     SECTION 12. Amended Definitions. As used in the Loan Agreement (including
all Exhibits thereto) and all other instruments and documents executed in
connection therewith, on and subsequent to the amendment Effective Date the term
(i) "Agreement" shall mean the Loan Agreement as amended by this Amendment, and
(ii) references to any and all other Credit Documents shall mean such documents
as amended as contemplated hereby.

                           [Intentionally Left Blank]

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<PAGE>

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

               NOTICE PURSUANT TO TEX. BUS. & COMM. CODE SS.26.02

     THIS AMENDMENT AND ALL OTHER CREDIT DOCUMENTS EXECUTED BY ANY OF THE
PARTIES BEFORE OR SUBSTANTIALLY CONTEMPORANEOUSLY WITH THE EXECUTION HEREOF
TOGETHER CONSTITUTE A WRITTEN LOAN AGREEMENT AND REPRESENT THE FINAL AGREEMENT
BETWEEN THE PARTIES AND MAY NOT BE CONTRADICTED BY EVIDENCE OF PRIOR,
CONTEMPORANEOUS OR SUBSEQUENT ORAL AGREEMENTS OF THE PARTIES. THERE ARE NO
UNWRITTEN ORAL AGREEMENTS BETWEEN THE PARTIES.

                         EVANS SYSTEMS, INC.,
                         a Texas corporation

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



                         CAIN, SMITH & STRONG, L.P,
                         a Delaware limited partnership

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

                                       5
<PAGE>

     The undersigned hereby join in the execution of this Amendment to evidence
their consent hereto and their acknowledgment that the Credit Documents executed
by the undersigned shall continue to apply to the Loan Agreement, as amended
hereby.

                                 CHEM-WAY SYSTEMS, INC.,
                                 a Texas corporation

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


                                 WAY ENERGY SYSTEMS, INC.,
                                 a Delaware corporation

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


                                 DIAMOND MINI MART, INC.,
                                 a Texas corporation

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


                                 EDCO, INC.,
                                 a Texas corporation

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

                                       6
<PAGE>

                                EVANS OIL COMPANY, INC.,
                                a Texas corporation

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



                                EDCO ENVIRONMENTAL SYSTEMS, INC.,
                                a Texas corporation

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



                                IN & OUT MINI MART, INC.,
                                a Texas corporation

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

                                       7
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                                 EXHIBITS A-D

                                    Omitted

                                       8
<PAGE>

                                 Schedules A-B

                                    Omitted

                                       12
<PAGE>

                                   Schedule B

                                 Trust Accounts

                                       13