<PAGE>

PORTIONS OF THIS EXHIBIT HAVE BEEN OMITTED PURSUANT TO A REQUEST FOR
CONFIDENTIAL TREATMENT PURSUANT TO RULE 24B-2 UNDER THE SECURITIES EXCHANGE ACT
OF 1934, AS AMENDED (THE "EXCHANGE ACT").  THESE OMITTED PORTIONS HAVE BEEN
MARKED WITH "***" AND HAVE BEEN FILED SEPARATELY WITH THE SECURITIES AND
EXCHANGE COMMISSION (THE "COMMISSION").

                                SITE LICENSE AGREEMENT

          This Site License Agreement (the "Agreement") is made and entered into
as of the 6th day of March, 1998, by and between Energy BioSystems Corporation,
a Delaware corporation ("EBC"), and Petro Star Inc., an Alaska corporation
("Petro Star").

                                 W I T N E S S E T H:

          WHEREAS, EBC owns or has developed certain proprietary technology and
know-how related to the removal of sulfur or other compounds or substances from
fossil fuels and their derivatives using genetically engineered microbes as
catalysts ("Biocatalysts"), processing performed on fossil fuels and their
derivatives using Biocatalysts, and derivatizations of sulfur compounds using
Biocatalysts (collectively, "Biorefining");
     
          WHEREAS, EBC desires to grant a license to Petro Star, and Petro Star
desires to obtain a license from EBC, for the use of EBC's Biorefining
technology for the removal of sulfur from diesel in a 5,000 barrel per day
biodesulfurization unit (the "BDS Unit") to be installed at Petro Star's Petro
Star Valdez Refinery located in Valdez, Alaska (the "PVSR");
     
          WHEREAS, EBC and Petro Star desire to establish an arrangement
pursuant to which EBC and Petro Star will cooperate with respect to the
installation, start-up and operation of the BDS Unit, the continued refinement
of the BDS Unit and EBC's use of the BDS Unit for the demonstration of EBC's
biodesulfurization technology to third parties;

          NOW, THEREFORE, in consideration of the foregoing and of the mutual
covenants, terms and conditions contained herein, the parties agree as follows:

                                     ARTICLE I
                                          
                        INSTALLATION AND OPERATION OF BDS UNIT

          Section  1.1   COOPERATIVE EFFORTS.  Petro Star and EBC will cooperate
with respect to the installation, start-up and operation of the BDS Unit, the
continued refinement of the BDS Unit and EBC's use of the BDS Unit for the
demonstration of EBC's biodesulfurization technology to third parties in
accordance with the plan attached hereto as Exhibit A (the "Installation and
Operation Plan") during the term of this Agreement.  The Installation and
Operation Plan will involve the following five phases of work, which may
overlap:

          (a)  the phase commencing with the execution of this Agreement and 
     ending with the completion of scoping economics (the "Initial Phase");


                                                         Site License Agreement

<PAGE>

          (b)  the phase commencing with the commencement of detailed
     engineering and ending at the completion of detailed engineering (the
     "Engineering Phase");

          (c)  the phase commencing with the commencement of construction of the
     BDS Unit and ending at the completion of construction of the BDS Unit (the
     "Construction Phase");

          (d)  the phase commencing with the completion of construction of the
     BDS Unit, involving the start-up of the BDS Unit and ending with the
     completion of the commencement of commercial operations (the "Start-up
     Phase"); and

          (e)  the phase commencing with the commencement of commercial
     operations and extending through the remaining term of the Agreement (the
     "Commercial Phase").


***

Each party shall use its respective diligent commercially reasonable efforts to
conduct the work and accomplish the goals of the Installation and Operation Plan
as contemplated thereby.

          Section  1.2   COORDINATION AND COMMUNICATION.  Petro Star and EBC
acknowledge that the cooperative efforts contemplated by this Agreement will
require the coordination of the respective efforts of and communication between
the two companies on an ongoing basis.


          Section  1.3   MANAGEMENT COMMITTEE.  Petro Star and EBC shall
establish a management committee whose members shall be responsible for managing
the respective efforts of the two companies under this Agreement (the
"Management Committee"), including but not limited to the coordination (as
between the parties) and management of the following matters:

          (a)  planning and implementation of efforts under the Installation 
     and Operation Plan;

          (b)  timely transfer of relevant information and progress reports in
     connection with the Installation and Operation Plan;

          (c)  changes to the Installation and Operation Plan as may be
     necessary or appropriate (which changes shall require the consensus of the
     members of the Management Committee);

          (d)  establishment of the criteria by which the commencement and
     completion of the various phases of the Installation and Operation Plan (as
     contemplated by Section 1.1) are to be determined; and

          (e)  protection of intellectual property developed as a result of the
     efforts of EBC and Petro Star under this Agreement.

Petro Star and EBC shall each appoint one member of its senior management and
one member of its senior technical staff to the Management Committee. 


*** This portion has been omitted based on a request for confidential treatment
pursuant to Rule 24b-2 of the Exchange Act.  The omitted portion has been
separately filed with the Commission.


                                     -2-                 Site License Agreement

<PAGE>


          Section  1.4   COMMITMENT OF PERSONNEL.  Petro Star and EBC will
commit such personnel to the efforts contemplated by this Agreement as may be
necessary or appropriate, as determined by the Management Committee in
accordance with the Installation and Operation Plan.  In addition, Petro Star
and EBC shall each assign a project coordinator (i) to act as a conduit for
timely transfer of relevant information and progress reports in connection with
the Installation and Operation Plan and (ii) to be responsible for managing its
day-to-day efforts under the Installation and Operation Plan.    ***


          Section  1.5   DEMONSTRATION OF BDS UNIT; EVALUATION AND TESTING. 
Petro Star will permit EBC and its licensees and prospective licensees to visit
and observe the operation of the BDS Unit during normal working hours and
subject to Petro Star's standard conditions for such visits.  EBC shall have the
right to employ the BDS Unit for Biorefining evaluation and testing (including,
without limitation, during the Commercial Phase)on such terms and conditions as
may be negotiated in good faith and agreed upon from time to time by EBC and
Petro Star.


          Section  1.6   NO AUTHORITY TO DIRECT ACTIONS OF THE OTHER PARTY. 
Although the parties acknowledge and agree that the coordination of their
respective efforts under this Agreement is essential, each party shall retain
the authority to direct, and the responsibility for, its own efforts under this
Agreement.  Nothing in this Article I shall be deemed to grant the Management
Committee the authority to direct the actions of either EBC or Petro Star.

                                     ARTICLE II

                                     SITE LICENSE

          Section  2.1   GRANT OF SITE LICENSE.  Subject to the terms and
conditions of this Agreement, including Petro Star's payment of the license fees
and royalties set forth in Section 2.2, EBC hereby grants to Petro Star during
the term of this Agreement, a limited, non-exclusive license to use the
Proprietary Technology (as defined herein) in the field of Biorefining that is
owned by or licensed to EBC (the "Licensed Technology") to construct and install
the BDS Unit at the PVSR, to conduct the development efforts contemplated by the
Installation and Operation Plan, to operate the BDS Unit at the PVSR for the
removal of sulfur from up to 5,000 barrels of diesel per day, and to make and
have made, use, sell and market and otherwise commercially exploit throughout
the world products of the PVSR processed by the BDS Unit.

          Section  2.2   SITE LICENSE FEES; ROYALTIES.  In consideration of the
license granted herein, Petro Star shall pay EBC the following amounts:

          (i)   a license fee of $200,000 payable upon the commencement of the
                Initial Phase;

          (ii)  a license fee of   ***

          (iii) a license fee of   ***

          (iv)  a license fee of   ***

          (v)   ***

*** This portion has been omitted based on a request for confidential treatment
pursuant to Rule 24b-2 of the Exchange Act.  The omitted portion has been
separately filed with the Commission.


                                     -3-                 Site License Agreement

<PAGE>

          Section 2.3    ***

          Section 2.4    ***

                                    ARTICLE III

                           RIGHTS TO INTELLECTUAL PROPERTY

          Section  3.1   OWNERSHIP AND DISCLOSURE OF EXISTING AND SEPARATELY
DEVELOPED PROPRIETARY TECHNOLOGY.  Both during and after the term of this
Agreement, EBC and Petro Star shall each retain their respective right, title
and interest in and to, and shall be the exclusive owner (as between the
parties) of, all technology, inventions, patents, patent rights, copyrights,
trade secrets and other proprietary rights and information ("Proprietary
Technology") owned or conceived by such party prior to the date of this
Agreement ("Existing Proprietary Technology") or separately developed by such
party during the term of this Agreement ("Separately Developed Proprietary
Technology").

          Section  3.2   OWNERSHIP OF JOINT PROPRIETARY TECHNOLOGY.  All
Proprietary Technology jointly developed during the term of this Agreement by
EBC and Petro Star ("Joint Proprietary Technology") shall be owned jointly by
EBC and Petro Star.

          Section  3.3   PATENT PROTECTION OF JOINT PROPRIETARY TECHNOLOGY.  EBC
shall have the authority, in its sole discretion, to decide whether to file, or
continue prosecution of, any patent application, or to maintain any patent
application or patent regarding the Joint Proprietary Technology.  If EBC
decides to take such actions with respect to any patent application or patent in
any country, EBC will pay all costs incident to such patent applications,
patents and like protection in such country regarding the Joint Proprietary
Technology, including  all costs incurred for filing, prosecution, issuance and
maintenance fees, as well as any costs incurred in filing continuations,
continuations-in-part, divisionals or related applications and any 
re-examination or reissue proceedings.  Petro Star shall provide EBC with 
reasonable assistance and cooperation with respect to the foregoing matters.

          Section  3.4   EBC'S EXCLUSIVE LICENSE TO JOINT PROPRIETARY TECHNOLOGY
FOR BIOREFINING.  EBC shall have and is hereby granted an exclusive, perpetual,
royalty-free, fully paid license to use all Joint Proprietary Technology in the
area of Biorefining, with rights to sublicense, and to develop, make and have
made, use, sell and market and otherwise commercially exploit products and
services throughout the world using such Joint Proprietary Technology in the
area of Biorefining.

          Section  3.5   EBC'S NON-EXCLUSIVE LICENSE TO PETRO STAR'S EXISTING
PROPRIETARY TECHNOLOGY AND SEPARATELY DEVELOPED PROPRIETARY TECHNOLOGY FOR
BIOREFINING.  Petro Star hereby grants to EBC both during and after the term of
this Agreement, a limited, non-exclusive, perpetual, royalty-free, fully-paid
license to use all Existing Proprietary Technology and Separately Developed
Technology of Petro Star in the area of Biorefining, with rights to sublicense,
and to develop, make and have made, use, sell and market and otherwise
commercially exploit products and services throughout the world using such
Existing Proprietary Technology and Separately Developed Proprietary Technology
in the area of Biorefining.


*** This portion has been omitted based on a request for confidential treatment
pursuant to Rule 24b-2 of the Exchange Act.  The omitted portion has been
separately filed with the Commission.


                                     -4-                 Site License Agreement

<PAGE>

          Section 3.6    ***

          Section 3.7    NO REVERSE ENGINEERING.  Each party agrees that it will
not, either during or after the term of this Agreement, conduct any genetic
analysis of or otherwise attempt to reverse engineer any Existing Proprietary
Technology or Separately Developed Proprietary Technology of the other party.

                                     ARTICLE IV

                                 TERM AND TERMINATION

          Section  4.1   TERM.  Unless earlier terminated by either party in
accordance with the provisions of this Article IV, the term of this Agreement
shall commence on the date of this Agreement and shall terminate on the earlier
of (i) the expiration of the last-to-expire patent licensed hereunder and (ii)
20 years from the effective date of this Agreement.

          Section  4.2   TERMINATION BY PETRO STAR.  Petro Star may without
liability terminate this Agreement (i) at the conclusion of the Initial Phase or
(ii) without cause  ***  upon the delivery of  ***  advance written notice to
EBC.

          Section  4.3   TERMINATION BY EITHER PARTY FOR CAUSE.  Either party
may terminate this Agreement upon the occurrence of any of the following events:

          (i)  the insolvency of the other party, or the making of an assignment
     for the benefit of creditors by the other party, the institution of 
     voluntary or involuntary bankruptcy proceedings on behalf of or against the
     other party or the appointment of a trustee or receiver with respect to a
     substantial portion of the other party's assets;

          (ii)  the failure by the other party to protect and maintain the
     confidentiality of Confidential Information as required by Article VI;

          (iii) the failure by the other party to submit to any inspection or
     audit or the repeated failure by a party to provide any information or
     report as required by Section 2.2 or 2.4;

          (iv)  the repeated failure of the other party to take such actions
     over a *** period (prior to the Commercial Phase) as are consistent with
     the terms of this Agreement and are commercially reasonable for such party
     to take and are required to facilitate the success of the Installation and
     Operation Plan, following the receipt of notice from the other party
     specifying in detail the nature of such actions; or

          (v)   the other party materially defaults in the performance of any
     material agreement, condition, covenant, representation or warranty of this
     Agreement, and such default or noncompliance shall not have been remedied,
     or steps initiated to remedy the same to the terminating party's reasonable
     satisfaction, within *** after receipt by the defaulting party of a
     written notice thereof from the terminating party.


*** This portion has been omitted based on a request for confidential treatment
pursuant to Rule 24b-2 of the Exchange Act.  The omitted portion has been
separately filed with the Commission.


                                     -5-                 Site License Agreement

<PAGE>

          Section  4.4   SURVIVAL.  Except to the extent expressly provided to
the contrary, the following provisions shall survive the termination of this
Agreement: ***, the audit rights set forth in Sections 2.2  ***, Articles III,
IV, V, VI, VIII, IX, X  and XI.  Any rights of EBC or Petro Star to payments
accrued through termination shall remain in effect following termination.

                                     ARTICLE V

                                        COSTS

          Except as provided on Article II of this Agreement, each party shall
each bear its own costs and expenses incurred in connection with the performance
of its obligations under this Agreement.

                                     ARTICLE VI

                                   CONFIDENTIALITY

          Section  6.1   CONFIDENTIAL INFORMATION.  For the purposes of this
Agreement, "Confidential Information" of a party shall mean (i) all Existing
Proprietary Technology of such party, (ii) all Separately Developed Proprietary
Technology of such party, and (iii) all other information, whether written, oral
or otherwise, containing or otherwise reflecting information directly or
indirectly concerning such party which such party will provide or has previously
provided to the other party to this Agreement. In addition, the term
"Confidential Information" shall mean and include all Joint Proprietary
Technology, which shall be deemed to be Confidential Information of both parties
to this Agreement.  Notwithstanding the foregoing, without granting any right or
license, the following will not constitute "Confidential Information" for
purposes of this Agreement:

          (a)  Information which is obtained by a party from a third person who
     is not prohibited from transmitting the information to such party by a 
     contractual, legal or fiduciary obligation to or on behalf of the other 
     party to this Agreement or its affiliates; 

          (b)   Information which is or becomes generally available to the
     public other than as a result of disclosure in violation of a contractual,
     legal or fiduciary obligation of a party to this Agreement, its employees,
     agents or representatives; 

          (c)   Information other than Joint Proprietary Technology which was
     in possession of a party prior to the disclosure thereof by the other
     party, its employees, agents or representatives; and

          (d)   Information developed by an employee or consultant of the
     receiving party who did not have access to the Confidential Information of
     the disclosing party.


*** This portion has been omitted based on a request for confidential treatment
pursuant to Rule 24b-2 of the Exchange Act.  The omitted portion has been
separately filed with the Commission.


                                     -6-                 Site License Agreement

<PAGE>

          Section  6.2   TREATMENT OF CONFIDENTIAL INFORMATION.  All
Confidential Information of a party shall be held and treated by the other party
in confidence and shall not, except as hereinafter provided, without the prior
written consent of the party providing such Confidential Information, be
disclosed by it in any manner whatsoever, in whole or in part, and will not be
used by it other than as provided by or as contemplated in this Agreement. 
Moreover, each of EBC and Petro Star agree (i) to disclose Confidential
Information only to its employees who need to know the Confidential Information
for the purpose of assisting it in carrying out the purposes and intent of this
Agreement and who agree to keep such information confidential and to be bound by
the terms of this Agreement to the same extent as if they were parties hereto,
(ii) that it will use its diligent efforts to cause all of such persons to act
in accordance herewith and be bound by this Agreement and (iii) that, in any
event, with respect to any such person that has not agreed in writing to be
bound by the terms of this Agreement, it shall be responsible for actions by any
such person that would constitute a breach of this Agreement to the same extent
as if such person were a party to this Agreement.

          Section  6.3   REQUIRED DISCLOSURE.  In the event that either party to
this Agreement is requested or required (by oral questions, interrogatories,
requests for information or documents, subpoena, civil investigative demand or
other process) to disclose any Confidential Information, such party will provide
the other party to this Agreement with immediate written notice of any such
request or requirement so that the other party to this Agreement at its own
expense may seek an appropriate protective order, seek the cooperation of the
party from which Confidential Information is requested or required to narrow the
request or requirement or waive compliance with the provisions of this
Agreement.  If, failing the entry of a protective order or the receipt of a
waiver hereunder, the party from which Confidential Information is requested or
required is, in the opinion of its counsel, compelled to disclose Confidential
Information, it may disclose only that portion of the Confidential Information
which its counsel advises it in writing that it is compelled to disclose and it
will exercise its diligent efforts to obtain assurance that confidential
treatment will be accorded such Confidential Information.  In any event, it will
not oppose action by the other party to obtain an appropriate protective order
or other reliable assurance that confidential treatment will be accorded the
Confidential Information.

          Section  6.4   RETURN OF CONFIDENTIAL INFORMATION.  In the event that
this Agreement is terminated for any reason and in any event within 30 days
after being so requested by the other party to this Agreement, each party shall
return to the other party all Confidential Information of the other party,
except for the portion of the Confidential Information which such party is
entitled to use under a continuing license under Article IV hereof or that may
be found in analyses, compilations, studies or other documents prepared by the
party required to return the Confidential Information.  That portion of the
Confidential Information which such party is entitled to use under a continuing
license under Article III hereof or that may be found in analyses, compilations,
studies or other documents prepared by such party and oral Confidential
Information will be held by such party in confidence in accordance with the
provisions of this Article VI.  Upon request by a party to this Agreement, an
authorized officer of such party may supervise such destruction.

          Section  6.5   REMEDIES FOR BREACH.  Each party acknowledges and
agrees that due to the unique nature of the other party's Confidential
Information, there can be no adequate remedy at law for any breach of its
obligations hereunder, that any such breach may allow the breaching party or
third parties to unfairly compete with such other party.  Accordingly, upon any
breach or any threat thereof with respect to the obligations of a party
hereunder with respect to the Confidential Information of the other party, such
other party shall be entitled to appropriate equitable relief in addition to
whatever remedies it might have at law and to be indemnified from any loss or
harm, including, without limitation, attorneys' fees, in connection with any
breach or enforcement of such party's obligation hereunder or the unauthorized
use or release of any such Confidential Information.


                                     -7-                 Site License Agreement

<PAGE>

          Section  6.6   DURATION OF CONFIDENTIALITY OBLIGATIONS.  The
obligations of the parties under this Article VI shall survive the termination
of this Agreement for a period of ***; PROVIDED that the termination of such
obligations shall not be deemed to constitute the license of any Confidential
Information.

                                    ARTICLE VII

                            REPRESENTATIONS AND WARRANTIES

          Section  7.1   REPRESENTATIONS AND WARRANTIES OF EBC.  EBC represents
and warrants to Petro Star as follows:

          (a)  EBC is a corporation duly organized, validly existing and in good
     standing under the laws of the State of Delaware.

          (b)   EBC has the full corporate power and authority to execute and
     deliver this Agreement and to perform its obligations hereunder.  The
     execution, delivery and performance of this Agreement have been duly and
     validly authorized by EBC, and upon execution and delivery, this Agreement
     will constitute a valid and binding agreement of EBC.

          (c)   Neither the execution and delivery of this Agreement nor the
     consummation of the transactions contemplated hereby does or will violate,
     conflict with, result in a breach of any material provision of, constitute
     a default under, or accelerate the performance required on the part of EBC
     by the terms of any judgment, order, decree or agreement, instrument or
     contract to or by which EBC or any of its assets is subject or bound.

          (d)   The execution and delivery of this Agreement does not require
     EBC to obtain any permits, authorizations or consents from any governmental
     body or from any other person, firm or corporation which have not been
     obtained, and such execution and delivery will not result in the breach of
     or give rise to any termination of any agreement or contract to which EBC
     may be a party.  The consummation of the transactions contemplated
     hereunder will not result in the breach of or give rise to any termination
     of any agreement or contract to which EBC may be a party.

          Section  7.2   REPRESENTATIONS AND WARRANTIES OF PETRO STAR.  Petro
Star represents and warrants to EBC as follows:

          (a)  Petro Star is a corporation duly organized, validly existing and
     in good standing under the laws of the State of Alaska.

          (b)  Petro Star has the full corporate power and authority to
     execute and deliver this Agreement and to perform its obligations
     hereunder.  The execution, delivery and performance of this Agreement have
     been duly and validly authorized by Petro Star, and upon execution and
     delivery, this Agreement will constitute a valid and binding agreement of
     Petro Star.


*** This portion has been omitted based on a request for confidential treatment
pursuant to Rule 24b-2 of the Exchange Act.  The omitted portion has been
separately filed with the Commission.


                                     -8-                 Site License Agreement

<PAGE>

          (c)   Neither the execution and delivery of this Agreement nor the
     consummation of the transactions contemplated hereby does or will violate,
     conflict with, result in a breach of any material provision of, constitute
     a default under, or accelerate the performance required on the part of
     Petro Star by the terms of any judgment, order, decree or agreement,
     instrument or contract to or by which Petro Star or any of its assets is
     subject or bound.

          (d)   The execution and delivery of this Agreement does not require
     Petro Star to obtain any permits, authorizations or consents from any
     governmental body or from any other person, firm or corporation which have
     not been obtained, and such execution and delivery will not result in the
     breach of or give rise to any termination of any agreement or contract to
     which Petro Star may be a party.  The consummation of the transactions
     contemplated hereunder will not result in the breach of or give rise to any
     termination of any agreement or contract to which Petro Star may be a
     party.

                                    ARTICLE VIII

                                   INDEMNIFICATION

          Section  8.1   BREACHES OF REPRESENTATIONS, WARRANTIES AND COVENANTS.
Each party shall indemnify, defend and hold harmless the other party and its
officers, directors and employees from and against any and all liabilities,
obligations, fees, including attorneys' fees and costs, expenses and losses
resulting from any breach of any representation or warranty or nonfulfillment of
any covenant on the part of the indemnifying party contained in this Agreement
or other instrument furnished or to be furnished by the indemnifying party
pursuant to this Agreement.

          Section  8.2   ACTIONS AND OMISSIONS.  Each party shall indemnify,
defend and hold harmless the other party and its officers, directors and
employees from and against any and all liabilities, obligations, fees, including
attorneys' fees and costs, expenses and losses incurred in connection with a
claim against the indemnified party based on any action or omission of the
indemnifying party or its agents or employees related to the obligations of the
indemnifying party under this Agreement.

          Section  8.3   INJURY AND DEATH.  Each party shall indemnify, defend
and hold harmless the other party and its officers, directors and employees from
and against any and all liabilities, obligations, fees, including attorney's
fees and costs, expenses and losses arising, or claimed to arise out of, or
which resulted from, or are claimed to result from any alleged injury or death,
or damage to property arising from or claimed to arise from, or which resulted
from, or are claimed to result from products and services of the indemnifying
party that incorporate or use Joint Proprietary Technology.


                                     -9-                 Site License Agreement

<PAGE>

                                     ARTICLE IX

                                     ARBITRATION

          In the event of any allegation of breach or question of interpretation
relating to this Agreement, EBC and Petro Star shall meet and negotiate in a
good faith effort to settle the matter amicably.  If the parties are unable to
settle the matter within *** after their first meeting, then upon the demand of
either EBC or Petro Star the matter shall be submitted to binding arbitration
with a single arbitrator, who shall be qualified in the subject matter of the
dispute.  The arbitration proceeding shall be governed by the rules of
arbitration promulgated by the American Arbitration Association and shall be
held in San Francisco, California. 

                                     ARTICLE X

                                       NOTICES

          Any communication, notice, request, consent, demand or statement
required or permitted hereunder shall be in writing and be given in person, by
express courier service or by means of telex, facsimile, or other wire
transmission (with request for assurance of receipt in a manner typical with
respect to communications of that type), and shall be deemed to have been given
(a) on delivery (if given in person or by express delivery) or (b) on the date
of transmission, if sent by telex, facsimile or other wire transmission,
addressed to a party at its address set forth below:

          In the case of EBC:

          President
          Energy BioSystems Corporation
          4200 Research Forest Drive
          The Woodlands, Texas  77381

          In the case of Petro Star:

          James F. Boltz
          Petro Star Inc. 
          201 Arctic Slope Avenue #200
          Anchorage, Alaska   99518

Each party hereto may change such address by giving prior written notice to the
other party as provided herein.


*** This portion has been omitted based on a request for confidential treatment
pursuant to Rule 24b-2 of the Exchange Act.  The omitted portion has been
separately filed with the Commission.


                                    -10-                 Site License Agreement

<PAGE>

                                     ARTICLE XI

                               MISCELLANEOUS PROVISIONS

          Section  11.1   ASSIGNMENT; SUCCESSORS AND ASSIGNS.  Neither party
shall assign this Agreement in whole or in part except in connection with the
transfer of all or substantially all of the stock or assets of such party or, in
the case of Petro Star, in connection with the transfer of a majority interest
in Petro Star Valdez, Inc. or the PVSR. Any assignment made or attempted in
violation of this Section 11.1 shall be void and of no effect.  This Agreement
shall be binding on, and shall inure to the benefit of, all successors and
assigns of the parties. 

          Section  11.2   GOVERNING LAW.  This Agreement shall be construed,
governed, interpreted and applied in accordance with the substantive, procedural
and arbitration laws of the State of Texas, without regard to the conflicts of
law principles thereof.

          Section  11.3   HEADINGS.  The titles and headings given to Articles
and Sections of this Agreement are provided only for convenience and shall not
be used in interpreting this Agreement.

          Section  11.4   ENTIRE AGREEMENT.  The parties acknowledge that this
Agreement sets forth the entire Agreement and understanding of the parties as to
the subject matter hereof, and shall not be subject to any change or
modification except by the execution of a written instrument subscribed to by
the parties.  All other previous or currently existing agreements and
understandings or other arrangements of any kind with respect to the said
subject matter shall be canceled and superseded completely by this Agreement as
of the date hereof. 

          Section  11.5   WAIVER.  The failure of either party to assert a right
hereunder or to insist upon compliance with any term or condition of this
Agreement shall not constitute a waiver of that right or excuse a similar
subsequent failure to perform any such term or condition by the other party.

          Section  11.6   COUNTERPARTS.  This Agreement may be executed in any
number of counterparts, each of which, when so executed and delivered, shall be
deemed to be an original, but all of such counterparts shall together constitute
one and the same instrument.

          Section  11.7   SEVERABILITY.  If any clause, paragraph, section,
article or part of this Agreement is held or declared to be void, invalid, or
illegal for any reason by any court of competent jurisdiction, the
ineffectiveness of such provision shall not in any way invalidate or affect any
other clause, paragraph, section, article or part of this Agreement, and this
Agreement shall be reformed consistent with the original objectives as stated
herein or therein.

          Section  11.8   NO AGENCY, PARTNERSHIP, ETC.  This Agreement shall
not constitute either party as a legal representative, joint venturer or agent
of the other, nor shall any party have the right or authority to assume, create
or incur any liability or any obligation of any kind, expressed or implied,
against or in the name or on behalf of any other party, unless otherwise
expressly permitted by the other party.

          Section  11.9   FURTHER ASSURANCES.  Each party hereto agrees to
execute, acknowledge and deliver such further instruments, and to do all such
other acts, as may be necessary or appropriate in order to carry out the
purposes and intent of this Agreement.


                                    -11-                 Site License Agreement

<PAGE>

          Section  11.10   PUBLIC STATEMENTS.  The parties shall consult with
each other prior to issuing any press release or any written public statement
with respect to this Agreement, and shall not issue any such press release or
written public statement prior to such consultation.

          IN WITNESS WHEREOF, the parties have duly executed this Agreement 
as of the day and year set forth above.


                                       ENERGY BIOSYSTEMS CORPORATION


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


                                       PETRO STAR INC.


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










                                    -12-                 Site License Agreement

<PAGE>

                                      EXHIBIT A

                           Installation and Operation Plan




                    ***



*** This portion has been omitted based on a request for confidential treatment
pursuant to Rule 24b-2 of the Exchange Act.  The omitted portion has been
separately filed with the Commission.






















                                     -13-                Site License Agreement