EXHIBIT 10.18

                                FIRST AMENDMENT

                                      to

                    AMENDED AND RESTATED GUARANTY AGREEMENT

                                      by

                              HOWELL CORPORATION,

                                 as Guarantor,

                                  in favor of

                               BANK OF MONTREAL,

                                   as Agent,



                         Effective as of July 26, 2001








      This FIRST  AMENDMENT TO AMENDED AND RESTATED  GUARANTY  AGREEMENT  (this
"First  Amendment")  executed  effective  as of the  26th of  July,  2001  (the
"Effective  Date") is by HOWELL  CORPORATION,  a  corporation  formed under the
laws of the State of Delaware (the  "Guarantor")  in favor of BANK OF MONTREAL,
as agent for the Lenders (in such capacity,  together with its successors,  the
"Agent").

                                   Recitals

      A.   Howell Petroleum  Corporation,  a corporation  formed under the laws
of Delaware  (the  "Borrower"),  the Agents and the Lenders  entered  into that
certain  Credit  Agreement  dated as of December  17, 1997 (the "Prior  Credit
Agreement").

      B.   In order to secure the  obligations of the Borrower under the Credit
Agreement,  the Guarantor  entered into that certain  Guaranty  Agreement dated
as of December 17, 1997 (the "Prior Guaranty Agreement").

      C.   The  Borrower,  the Agents the  Lenders  entered  into that  certain
Amended  and  Restated  Credit  Agreement  dated as of  December  1,  1998 (the
"Amended and Restated  Credit  Agreement")  amending  and  restating  the Prior
Credit Agreement.

      D.   In order  to  secure  the  obligations  of the  Borrower  under  the
Amended  and  Restated  Credit  Agreement,  the  Guarantor  entered  into  that
certain  Amended and Restated  Guaranty  Agreement dated as of December 1, 1998
(the "Amended and Restated Guaranty Agreement").

      E.   The  Borrower  has  requested  and the Agents and the  Lenders  have
agreed  to  amend  certain  provisions  of  the  Amended  and  Restated  Credit
Agreement and the Amended and Restated Guaranty Agreement.

      F.   NOW,  THEREFORE,  in  consideration  of the  premises and the mutual
covenants herein contained,  for good and valuable  consideration,  the receipt
and sufficiency of which are hereby  acknowledged,  the parties hereto agree as
follows:

      Section 1.Defined Terms.  Each  capitalized  term which is defined in the
Amended and Restated Credit  Agreement,  but which is not defined in this First
Amendment,  shall  have the  meaning  ascribed  such  term in the  Amended  and
Restated   Credit   Agreement.   Unless   otherwise   indicated,   all  section
references in this First Amendment  refer to the Amended and Restated  Guaranty
Agreement.

      Section 2.Amendments to the Amended and Restated GuarantyAgreement.

      2.1  Amendments to Section 1.2. The  following  new  definition is hereby
           -------------------------
added where alphabetically appropriate:

           "Net Cash  Proceeds"  shall mean,  with  respect to any sale or
      disposition  of  securities,   the  cash  proceeds  (including  cash
      equivalents  and  any  cash  payments  received  by way of  deferred
      payment of principal  pursuant to a note or  installment  receivable
      or purchase price  adjustment  receivable or otherwise,  but only as
      and when  received)  of such sale or other  disposition  received by
      the Guarantor or any of its  Consolidated  Subsidiaries,  net of all
      attorneys'  fees,  accountants'  fees,  investment  banking fees and
      other  customary  fees  and  commissions  actually  incurred  by the
      Guarantor or any of its Consolidated  Subsidiaries and documented in
      connection therewith.

      2.2  Amendments  to  Section  5.3.  Section  5.3  is  hereby  amended  by
deleting  such  section in its  entirety  and  inserting  in lieu  thereof  the
following:

           5.3  Minimum   Tangible  Net  Worth.  The  Guarantor  will  not
      permit  its  Tangible  Net Worth at any time to be less than the sum
      (without  duplication)  of (i)  $33,050,000  (85% of the Guarantor's
      Tangible  Net Worth as of December 31,  2000),  plus (ii) 50% of the
      Net Cash  Proceeds  of any primary  offering  (public or private) of
      equity  securities  consummated  by the  Guarantor  after  the First
      Amendment  Effective Date, plus (iii) 50% of Consolidated Net Income
      for each fiscal  quarter of the Guarantor  ending after December 31,
      2000 (to the extent for any such  fiscal  quarter  Consolidated  Net
      Income is positive).

      2.3  Amendments  to  Section  5.4.  Section  5.4  is  hereby  amended  by
deleting  such  section in its  entirety  and  inserting  in lieu  thereof  the
following:

           5.4  Current Ratio.  The Guarantor's  ratio of (i) consolidated
      current  assets  plus  availability   under  the  Facility  to  (ii)
      consolidated  current  liabilities  (excluding current maturities of
      the Notes) shall not at any time be less than 1.0 to 1.0.

      Section 3.Miscellaneous.
                -------------

      3.1  Confirmation.  The  provisions of the Amended and Restated  Guaranty
Agreement (as amended by this First  Amendment)  shall remain in full force and
effect in accordance with its terms following the  effectiveness  of this First
Amendment.

      3.2  Counterparts.  This First  Amendment  may be executed by one or more
of the parties hereto in any number of separate  counterparts,  and all of such
counterparts  taken  together  shall be deemed to  constitute  one and the same
instrument.

      3.3  No Oral  Agreement.  THIS WRITTEN FIRST  AMENDMENT,  THE AMENDED AND
RESTATED  GUARANTY   AGREEMENT  AND  THE  OTHER  LOAN  DOCUMENTS   EXECUTED  IN
CONNECTION  HEREWITH AND THEREWITH  REPRESENT THE FINAL  AGREEMENT  BETWEEN THE
PARTIES AND MAY NOT BE CONTRADICTED BY EVIDENCE OF PRIOR,  CONTEMPORANEOUS,  OR
UNWRITTEN  ORAL  AGREEMENTS  OF  THE  PARTIES.  THERE  ARE NO  SUBSEQUENT  ORAL
AGREEMENTS BETWEEN THE PARTIES.

      3.4  Governing  Law.  THIS FIRST  AMENDMENT  (INCLUDING,  BUT NOT LIMITED
           --------------
TO,  THE  VALIDITY  AND  ENFORCEABILITY  HEREOF)  SHALL  BE  GOVERNED  BY,  AND
CONSTRUED IN ACCORDANCE WITH, THE LAWS OF THE STATE OF TEXAS.





                [SIGNATURE PAGE - FIRST AMENDMENT TO
                   AMENDED AND RESTATED GUARANTY AGREEMENT]

      IN WITNESS  WHEREOF,  the parties hereto have caused this First Amendment
to be duly executed effective as of the date first written above.


GUARANTOR:                                          HOWELL CORPORATION


                               By:   /s/ ALLYN R. SKELTON
                                     --------------------
                                     Allyn R. Skelton, Vice President &
                                     Chief Financial Officer



AGENT:                         BANK OF MONTREAL, AS AGENT



                               By:   /s/ JAMES DUCOTE
                                     -----------------------------
                                     James Ducote, Vice President