Document:

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                                                                    EXHIBIT 10.6

                         RIO VISTA ENERGY PARTNERS L.P.
                              UNIT OPTION AGREEMENT

                            Void after July 10, 2006

Option No. ___                                      Date of Grant: July 10, 2003

         FOR VALUE RECEIVED and pursuant to the terms of a letter agreement
dated November 29, 2002, between Shore Capital LLC and Penn Octane Corporation,
a Delaware corporation ("Penn Octane"), and a resulting employment agreement
dated May 13, 2003, between Penn Octane and Richard Shore, Jr., the undersigned,
RIO VISTA ENERGY PARTNERS L.P., a limited partnership organized and existing
under the laws of the State of Delaware, hereby certifies that Shore Capital LLC
is entitled, subject to the terms set forth below, to purchase from the
Partnership after the completion of the distribution by Penn Octane to its
stockholders of all of the outstanding Common Units of the Partnership and
before 5:00 P.M. New York time, on July 10, 2006 (the "Expiration Date"), 97,415
Common Units of the Partnership. The purchase price per Common Unit shall be
$8.47 (the "Exercise Price").

         The details of this Option Agreement (this "Agreement") are as follows:

         1. DEFINITIONS.

                  (a) "AFFILIATE" means, with respect to any specified person,
any person that directly or through one or more intermediaries controls or is
controlled by or is under common control with the specified person. As used in
this definition, the term "control" means the possession, directly or
indirectly, of the power to direct or cause the direction of the management and
policies of a person, whether through ownership of voting securities, by
contract or otherwise. For purposes of clarification, Penn Octane Corporation is
an Affiliate of the Partnership and the General Partner.

                  (b) "CODE" means the Internal Revenue Code of 1986, as
amended.

                  (c) "GENERAL PARTNER" means Rio Vista GP LLC, a Delaware
limited liability company, and its successors or assigns.

                  (d) "MANAGER" means a manager of the General Partner under the
Delaware Limited Liability Company Act.

                  (e) "OFFICER" means any person designated by the General
Partner as an officer.

                  (f) "OPTION" means an option to acquire Common Units granted
pursuant to this Agreement.

<PAGE>

                  (g) "OPTIONHOLDER" means the person to whom an Option to
acquire Common Units is granted pursuant to this Agreement.

                  (h) "PARTNERSHIP" means Rio Vista Energy Partners L.P., a
Delaware limited partnership, and its successors or assigns.

                  (i) "PARTNERSHIP AGREEMENT" means the limited partnership
agreement of the Partnership, as amended.

                  (j) "PURCHASE PRICE" means the amount equal to the product of
the Exercise Price and the number of Common Units to be purchased upon exercise
of this Option.

                  (k) "COMMON UNIT" has the meaning set forth in the Partnership
Agreement or any equity interest into which a Common Unit is exchanged or
converted.

         2. ADMINISTRATION.

                  (a) ADMINISTRATION BY GENERAL PARTNER. The General Partner
shall administer this Agreement. Any interpretation of this Agreement by the
General Partner and any decision by the General Partner under this Agreement
shall be final and binding on all persons.

                  (b) POWERS OF GENERAL PARTNER. The General Partner shall have
the power, subject to, and within the limitations of, the express provisions of
this Agreement:

                           (i) to construe and interpret this Agreement, and to
establish, amend and revoke rules and regulations for its administration; the
General Partner, in the exercise of this power, may correct any defect, omission
or inconsistency in this Agreement, in a manner and to the extent it shall deem
necessary or expedient to make this Agreement fully effective; and

                           (ii) generally, to exercise such powers and to
perform such acts as the General Partner deems necessary or expedient to promote
the best interests of the Partnership which are not in conflict with the
provisions of this Agreement.

         3. NUMBER OF COMMON UNITS, EXERCISE PRICE AND CAPITALIZATION
ADJUSTMENTS. The number of Common Units subject to this Option and the exercise
price per Common Unit may be adjusted from time to time for capitalization
adjustments described in this Section. If any change is made in the Common Units
subject to this Agreement, without the receipt of consideration by the
Partnership (through conversion, merger, consolidation, reorganization,
recapitalization, unit distribution, distribution in property other than cash,
Common Units split, liquidating distribution, combination of Common Units,
exchange of Common Units, change in structure or other transaction not involving
the receipt of consideration by the Partnership), the Common Units subject to
this Agreement will be appropriately adjusted in the class(es) and number of
securities and price per Common Unit. The General Partner, the determination of
which shall be final, binding and conclusive, shall make such adjustments. (The
conversion of any convertible securities of the Partnership shall not be treated
as a transaction "without receipt of consideration" by the Partnership.)

         4. METHOD OF PAYMENT. Payment of the Purchase Price is due in full upon
exercise of all or any part of this Option. The Optionholder may elect to make
payment of the Purchase Price in cash or by check.

                                      -2-
<PAGE>

         5. WHOLE COMMON UNITS. This Option may only be exercised for whole
Common Units.

         6. SECURITIES LAW COMPLIANCE. Notwithstanding anything to the contrary
contained herein, this Option may not be exercised unless the Common Units
issuable upon exercise of this Option are then registered under the Securities
Act or, if such Common Units are not then so registered, the Partnership has
determined that such exercise and issuance would be exempt from the registration
requirements of the Securities Act. The Partnership shall use its commercially
reasonable efforts to register such Common Units under the Securities Act.

         7. TERM. The term of this Option commences on the date Penn Octane
completes the distribution to its stockholders of all the outstanding Common
Units of the Partnership and expires on the Expiration Date.

         8. EXERCISE.

                  (a) Subject to Section 8(c), the Optionholder may exercise
this Option during its term by delivering a Notice of Exercise (in a form
designated by the General Partner) together with the Purchase Price to the
Secretary of the General Partner, or to such other person as the General Partner
may designate, during regular business hours, together with such additional
documents as the General Partner may then require.

                  (b) By exercising this Option, the Optionholder agrees that,
as a condition to any exercise of this Option, the Partnership or the General
Partner may require the Optionholder to enter an arrangement providing for the
payment by the Optionholder to the Partnership of any tax withholding obligation
of the Partnership, as reasonably determined by the Partnership, arising by
reason of (1) the exercise of this Option, or (2) the disposition of Common
Units acquired upon such exercise.

                  (c) Notwithstanding anything herein to the contrary, during
the term of this Option, this Option may only be exercised during the first ten
(10) days of the first month of each fiscal quarter of the Partnership and
during such other periods as the General Partner may designate in its sole
discretion for purposes of minimizing the accounting costs to the Partnership
resulting from such exercise.

         9. TRANSFERABILITY. This Option is not transferable, except to any
Affiliate of the Optionholder, and is exercisable only by the Optionholder or
such Affiliate. The transferability of the Common Units issued upon exercise of
this Option shall be subject to the conditions, restrictions and limitations set
forth in this Agreement, the Partnership Agreement and any other agreements the
Optionholder may have with the Partnership.

                  (a) The provisions of this Section 9 may be waived with
respect to any transfer by the Partnership, upon duly authorized action of the
General Partner.

                  (b) Any sale or transfer, or purported sale or transfer, of
the Common Units by the Optionholder shall be null and void unless the terms,
conditions, and provisions of this Section 9 are observed and followed.

                                      -3-
<PAGE>

         10. WITHHOLDING OBLIGATIONS

                  (a) At the time this Option is exercised, in whole or in part,
or at any time thereafter as requested by the Partnership, you hereby authorize
withholding from payroll and any other amounts payable to you, and otherwise
agree to make adequate provision for, any sums required to satisfy the federal,
state, local and foreign tax withholding obligations of the Partnership or an
Affiliate, if any, which arise in connection with this Option.

                  (b) This Option is not exercisable unless the tax withholding
obligations of the Partnership and/or any Affiliate are satisfied. Accordingly,
you may not be able to exercise this Option when desired even though this Option
is vested, and the Partnership shall have no obligation to issue a certificate
for such Common Units or release such Common Units from any escrow provided for
herein.

         11. TAX CONSEQUENCES AND CAPITAL ACCOUNT UPON EXERCISE OF OPTION. It is
intended that neither the Optionholder, the Partnership nor any of the partners
(owners) of the Partnership shall have any federal income tax consequences upon
grant of this Option, or, except as described herein, upon exercise of this
Option. Additionally, it is intended that the Optionholder shall not be treated
as a partner with respect to the Common Units subject to this Agreement until
such time as this Option is exercised. It is intended that, upon exercise of
this Option, the Optionholder shall include in income ("Exercise Income") in the
tax year of exercise an amount equal to the excess, if any, of the fair market
value of Common Units on the date of exercise over the sum of the amount the
Optionholder has paid or will pay to the Partnership ("Option Consideration")
upon the grant and exercise of the Option. It is intended that the Partnership
shall be entitled to a deduction equal to the amount of Exercise Income, which,
if the Partnership continues to be a partnership for federal income tax
purposes, shall be allocated solely to the partners of the Partnership other
than the Optionholder to whom the Exercise Income is attributable. Upon exercise
of this Option, Optionholder shall receive a positive capital account in the
Partnership (assuming the Partnership continues to be classified as a
partnership for federal income purposes) equal to the sum of the Exercise Income
to the Optionholder and the amount of Option Consideration paid by the
Optionholder. Should the federal income tax consequences differ from that
described in this section, the General Partner shall have the authority to
change the capital account or allocations of income and deduction to the
Optionholder as described herein in manner which in its discretion most closely
achieves the same economic effect of the consequences described in this Section.
Notwithstanding anything herein to the contrary, the General Partner shall have
the authority to change the tax reporting described above with respect to the
issuance or exercise of this Option or alter the capital accounts or allocations
of Partnership items as necessary to preserve or achieve the uniformity of
Common Units.

         12. NOTICES. Any notices provided for in this Option or this Agreement
shall be given in writing and shall be deemed effectively given upon receipt or,
in the case of notices delivered by the Partnership to the Optionholder, five
(5) days after deposit in the United States mail, postage prepaid, addressed to
the Optionholder at the last address provided to the Partnership.

                                      -4-
<PAGE>

         13. THIS AGREEMENT; PARTNERSHIP AGREEMENT. This Option is subject to
all the provisions of this Agreement, the provisions of which are hereby made a
part of this Option, and is further subject to all interpretations, amendments,
rules and regulations which may from time to time be promulgated and adopted
pursuant to this Agreement, and the Common Units to be delivered are subject to
the terms of the Partnership Agreement. In the event of any conflict among
Optionholder's rights under the Common Units, this Agreement and the Partnership
Agreement, the terms of the Partnership Agreement shall control.

         14. MISCELLANEOUS.

                  (a) AVAILABILITY OF COMMON UNITS. During the term of this
Option, the Partnership shall keep available at all times the number of Common
Units required to satisfy the Option.

                  (b) PARTNER RIGHTS. No Optionholder shall be deemed to be
partner of the Partnership, or to have any of the rights of a partner or rights
of an assignee from a partner with respect to, any Common Units subject to the
Option unless and until such Optionholder has satisfied all requirements for
exercise of the Option pursuant to its terms.

                  (c) INVESTMENT ASSURANCES. Unless the Common Units issuable
upon exercise of this Option are then registered under the Securities Act, the
General Partner may require an Optionholder, as a condition of exercising or
acquiring Common Units under the Option, to give written assurances that he is
an "accredited investor," as defined in the rules and regulations under the
Securities Act. The General Partner may, upon advice of counsel to the General
Partner, place legends on Common Units certificates issued under the Option as
such counsel deems necessary or appropriate in order to comply with applicable
securities laws, including, but not limited to, legends restricting the transfer
of the Common Units.

                  (d) PARTNERSHIP AGREEMENT. Before receiving Common Units, the
Optionholder shall take such action and execute such documents as the General
Partner may require to become a partner of the Partnership.

         IN WITNESS WHEREOF, this Option Agreement has been duly executed by the
parties hereto as of the Date of Grant.

                                  RIO VISTA ENERGY PARTNERS L.P.

                                  By:  RIO VISTA GP LLC, general partner

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

ACCEPTED AND AGREED:

SHORE CAPITAL LLC

By:
   ----------------------------------
     Richard Shore, Jr., President

                                      -5-<PAGE>
                                                                    EXHIBIT 10.8

                                RIO VISTA GP LLC

                                VOTING AGREEMENT

                              ______________, 2004

<PAGE>

                                VOTING AGREEMENT

         This Voting Agreement (this "AGREEMENT") is entered into as of
____________, 2004, by and among Rio Vista GP LLC, a Delaware limited liability
company (the "COMPANY"), Penn Octane Corporation, a Delaware corporation and
member of the Company ("PENN OCTANE"), and the members of the Company identified
on the signature page of this Agreement (collectively, the "MEMBERS" and,
individually, each a "MEMBER"). The Company, Penn Octane and the Members are
sometimes referred to herein, collectively, as the "parties" and, individually,
as a "party" to this Agreement. Unless otherwise provided, capitalized terms
used in this Agreement have the meanings ascribed to them in Section 5 hereof.

                                    RECITALS

         WHEREAS, immediately prior to the date hereof, Penn Octane was the
owner of on hundred percent (100%) of the limited liability company interests of
the Company (the "PENN OCTANE INTEREST").

         WHEREAS, pursuant to option agreements dated July 10, 2003, Penn Octane
granted each Member the right (the "PURCHASE RIGHT") to purchase twenty-five
percent (25%) of the Penn Octane Interest at an exercise price equal to the pro
rata portion of the tax basis capital the Partnership (as defined in Section 1.4
of this Agreement) after the distribution of the common units of the Partnership
to the stockholders of Penn Octane.

         WHEREAS, the exercise of the Purchase Right is conditioned upon the
execution and delivery of this Agreement by each Member.

                                    AGREEMENT

         NOW, THEREFORE, in consideration of the mutual promises,
representations, warranties, covenants, and conditions set forth in this
Agreement, the Purchase Right and for other good and valuable consideration, the
receipt and sufficiency of which is hereby acknowledged, the Parties hereby
agree as follows:

1. VOTING AGREEMENT.

         1.1 Voting by Member for Managers. From and after the date hereof and
until the provisions of this Section 1 cease to be effective, at each meeting of
the members of the Company, or at any meeting of the members of the Company at
which members of the Board of Managers of the Company (the "BOARD") are to be
elected, or whenever members of the Board are to be elected by the members of
the Company by written consent, each Member agrees to vote or act with respect
to all of his, her or its limited liability company interests in the Company and
shall take all other necessary or desirable actions within such Member's control
whether in such capacity as a Member, manager of the Company, officer of the
Company, or otherwise (including, without limitation, attendance at meetings, in
person or by proxy, for purposes of

<PAGE>

obtaining a quorum and execution of written consents), and the Company agrees to
take all necessary and desirable actions within its control, so as to:

         1.1.1 fix the number of members of the Board (the "MANAGERS" and each,
individually, a "MANAGER") at such number designated by Penn Octane; and

         1.1.2 elect each and every Manager designated by Penn Octane.

         1.2 Removal and Substitution of Members of the Board. Each Member
agrees to vote or act with respect to all of his, her or its limited liability
company interests in the Company for the removal of any member of the Board upon
the request of Penn Octane and for the election to the Board of a substitute
nominated by Penn Octane in accordance with the provisions of Section 1.1. Each
Member agrees that no Manager may be removed from office without the approval of
Penn Octane. Each Member further agrees to vote or act with respect to all of
his, her or its limited liability company interests in the Company in such
manner as shall be necessary or appropriate to ensure that any vacancy on the
Board occurring for any reason shall be filled only in accordance with the
provisions of Section 1.1.

         1.3 Voting by Member on All Other Matters. From and after the date
hereof and until the provisions of this Section 1 cease to be effective, at each
meeting of the members of the Company, or whenever members of the Company are to
take action by written consent, each Member agrees to vote or act with respect
to all of his, her or its limited liability company interests in the Company as
directed by Penn Octane and shall take all other necessary or desirable actions
within such Member's control whether in such capacity as a Member, Manager,
officer of the Company, or otherwise (including, without limitation, attendance
at meetings, in person or by proxy, for purposes of obtaining a quorum and
execution of written consents), and the Company agrees to take all necessary and
desirable actions within its control, as directed by Penn Octane.

         1.4 Exceptions. The provisions of Section 1.3 of this Agreement do not
apply with respect to any matter involving (a) the sale, transfer, assignment,
pledge, hypothecation or other disposal of all or any portion of (i) any general
partner interest (the "GENERAL PARTNER INTEREST") in Rio Vista Energy Partners
L.P., a Delaware limited partnership (the "PARTNERSHIP"), or (ii) any Incentive
Distribution Rights (as defined in the First Amended and Restated Agreement of
Limited Partnership of Rio Vista Energy Partners L.P. (the "PARTNERSHIP
AGREEMENT")) or (b) the merger, consolidation or sale of all or substantially
all of the assets of the Partnership, its subsidiaries or the Company.

2. NO REVOCATION. The voting agreements contained herein are coupled with an
interest and may not be revoked during the term of this Agreement.

3. LEGEND. Each certificate evidencing limited liability company interests in
the Company and each certificate issued in exchange for or upon the Transfer, as
defined in Section 5 below, of any limited liability company interests of the
Company will be stamped or otherwise imprinted with a legend in substantially
the following form:

                  "THE SECURITIES REPRESENTED BY THIS CERTIFICATE ARE SUBJECT TO
                  A VOTING AGREEMENT DATED AS OF ______________, 2003, ENTERED
                  INTO BY AND AMONG THE COMPANY, PENN OCTANE AND CERTAIN OF THE
                  COMPANY'S MEMBERS, AND BY ACCEPTING THESE SECURITIES, THE
                  PERSON ACCEPTING SUCH INTEREST SHALL BE DEEMED TO AGREE TO AND
                  SHALL BECOME BOUND BY ALL THE PROVISIONS OF SAID VOTING
                  AGREEMENT. A COPY OF SUCH VOTING AGREEMENT WILL BE FURNISHED,
                  WITHOUT CHARGE, BY THE COMPANY TO THE HOLDER HEREOF UPON
                  WRITTEN REQUEST."

The Company will imprint such legend on all certificates representing limited
liability company interests outstanding prior to the date hereof.

<PAGE>

4. TRANSFER. Prior to any Transfer of any limited liability company interest in
the Company or any interest therein to any Person, which Transfer is subject to
the restrictions set forth in the Agreements, the Member effecting such Transfer
will cause the prospective Transferee(s) to execute and deliver to each Party a
counterpart of this Agreement.

5. DEFINITIONS. As used in this Agreement, the following terms shall have the
meanings set forth below:

         5.1 "PERSON" means an individual, a partnership, a corporation, a
limited liability company, an association, a joint stock company, a trust, a
joint venture, an unincorporated organization, and a governmental entity or any
department, agency, or political subdivision thereof.

         5.2 "TRANSFER" means the sale, transfer, assignment, pledge,
hypothecation or other disposal.

         5.3 "TRANSFEREE" shall mean the recipient of a transfer.

6. MISCELLANEOUS.

         6.1 Notices. All notices and other communications required or permitted
hereunder shall be in writing and shall be mailed by registered or certified
mail, postage prepaid, sent by facsimile or electronic mail or otherwise
delivered by hand or by messenger addressed as follows:

                  (1) if to a Member or Penn Octane, at the Member's or Penn
Octane's, as applicable, address, facsimile number or electronic mail address as
shown in the Company's records, as may be updated in accordance with the
provisions hereof.

                  (2) if to the Company, one copy should be sent to its address
or facsimile number set forth on the signature page of this Agreement and
addressed to the attention of the President, or at such other address or
facsimile number as the Company shall have furnished to the Members.

<PAGE>

Each such notice or other communication shall for all purposes of this Agreement
be treated as effective or having been given when delivered if delivered
personally, or, if sent by mail, at the earlier of its receipt or 72 hours after
the same has been deposited in a regularly maintained receptacle for the deposit
of the United States mail, addressed and mailed as aforesaid or, if sent by
facsimile, upon confirmation of facsimile transfer.

         6.2 Successors and Assigns. Except as otherwise provided herein, the
terms and conditions of this Agreement shall inure to the benefit of and be
binding upon the respective successors and assigns of the parties. Nothing in
this Agreement, express or implied, is intended to confer upon any party other
than the parties hereto or their respective successors and assigns any rights,
remedies, obligations or liabilities under or by reason of this Agreement,
except as expressly provided in this Agreement.

         6.3 Severability. In the event that any provision of this Agreement
becomes or is declared by a court of competent jurisdiction to be illegal,
unenforceable or void, this Agreement shall continue in full force and effect
without said provision, and the parties agree to negotiate, in good faith, a
legal and enforceable substitute provision which most nearly effects the
parties' intent in entering into this Agreement.

         6.4 Amendments and Waivers. Any term of this Agreement may be amended
and the observance of any term of this Agreement may be waived (either generally
or in a particular instance and either retroactively or prospectively), only
with the written consent of (i) the Company, (ii) each Member and (iii) Penn
Octane. Any such amendment, waiver, discharge or termination effected in
accordance with this paragraph shall be binding upon each holder of any
securities purchased under this Agreement at the time outstanding (including
securities into which such securities have been converted or exchanged or for
which such securities have been exercised) and each future holder of all such
securities.

         6.5 Governing Law. This Agreement shall be governed by and construed
under the laws of the State of Delaware as applied to agreements among Delaware
residents entered into and to be performed entirely within Delaware.

         6.6 Specific Performance. The rights of the parties under this
Agreement are unique and, accordingly, the parties shall, in addition to such
other remedies as may be available to any of them at law or in equity, have the
right to enforce their rights hereunder by actions for specific performance to
the extent permitted by law.

         6.7 Counterparts. This Agreement may be executed in any number of
counterparts, each of which, when so executed and delivered, will be deemed an
original, and all such counterparts together will constitute one and the same
instrument.

         6.8 Conflict. In the event of any conflict between the terms of this
Agreement and the Company's Limited Liability Company Agreement, the Partnership
Agreement or any other agreement to which the Company, Penn Octane or a Member
is bound, the terms of this Agreement will control.

         6.9 Attorney's Fees. In the event that any suit or action is instituted
to enforce any provision in this Agreement, the prevailing party in such dispute
shall be entitled to recover from

<PAGE>

the losing party all fees, costs and expenses of enforcing any right of such
prevailing party under or with respect to this Agreement, including without
limitation, such reasonable fees and expenses of attorneys and accountants,
which shall include, without limitation, all fees, costs and expenses of
appeals.

         6.10 Titles and Subtitles. The titles and subtitles used in this
Agreement are used for convenience only and are not to be considered in
construing or interpreting this Agreement. All references in this Agreement to
sections, paragraphs, exhibits and schedules shall, unless otherwise provided,
refer to sections and paragraphs hereof and exhibits and schedules attached
hereto.

         6.11 Entire Agreement. This Agreement constitutes the full and entire
understanding and agreement among the parties with regard to the subject matter
hereof and supercedes and replaces any prior verbal or written understandings,
communications, or representations between the Parties in relation to the
subject matter of this Agreement.

         6.12 Construction. The parties hereto have participated jointly in the
negotiation and drafting of this Agreement. In the event an ambiguity or
question of intent or interpretation arises, this Agreement shall be construed
as if drafted jointly by the parties hereto and no presumption or burden of
proof shall arise favoring or disfavoring any party hereto by virtue of the
authorship of any of the provisions of this Agreement. Any reference to any
federal, state, local, or foreign statute or law shall be deemed also to refer
to all rules and regulations promulgated thereunder, unless the context requires
otherwise.

         6.13 Delays or Omissions. Except as expressly provided herein, no delay
or omission to exercise any right, power or remedy accruing to any party to this
Agreement upon any breach or default of any other party under this Agreement
shall impair any such right, power or remedy of such non-defaulting party, nor
shall it be construed to be a waiver of any such breach or default, or an
acquiescence therein, or of or in any similar breach or default thereafter
occurring, nor shall any waiver of any single breach or default be deemed a
waiver of any other breach or default theretofore or thereafter occurring. Any
waiver, permit, consent or approval of any kind or character on the part of any
party of any breach or default under this Agreement, or any waiver on the part
of any party of any provisions or conditions of this Agreement, must be in
writing and shall be effective only to the extent specifically set forth in such
writing. All remedies, either under this Agreement or by law or otherwise
afforded to any party to this Agreement, shall be cumulative and not
alternative.

         6.14 Telecopy Execution and Delivery. A facsimile, telecopy or other
reproduction of this Agreement may be executed by one or more parties hereto,
and an executed copy of this Agreement may be delivered by one or more parties
hereto by facsimile or similar electronic transmission device pursuant to which
the signature of or on behalf of such party can be seen, and such execution and
delivery shall be considered valid, binding and effective for all purposes. At
the request of any party hereto, all parties hereto agree to execute an original
of this Agreement as well as any facsimile, telecopy or other reproduction
hereof.

<PAGE>

         6.15 Jurisdiction; Venue. With respect to any disputes arising out of
or related to this Agreement, the parties consent to the exclusive jurisdiction
of, and venue in, the state or federal courts in Harris County in the State of
Texas.

         6.16 Jury Trial. EACH OF THE PARTIES HERETO HEREBY IRREVOCABLY WAIVES,
TO THE FULLEST EXTENT PERMITTED BY LAW, ANY AND ALL RIGHT TO TRIAL BY JURY IN
ANY LEGAL PROCEEDING (WHETHER SOUNDING IN CONTRACT, TORT OR OTHERWISE) ARISING
OUT OF OR RELATED TO THIS AGREEMENT.

         6.17 Further Assurances; Instruments. Each of the Members, Penn Octane
and the Company agree not to vote any of their respective limited liability
interests in the Company, or to take any other actions, that would in any manner
defeat, impair, be inconsistent with or adversely affect the rights of the
parties under Section 1 of this Agreement. From time to time, each party hereto
shall execute and deliver such instruments and documents as may be reasonably
necessary to carry out the purposes and intent of this Agreement.

<PAGE>

         IN WITNESS WHEREOF, the undersigned or each of their respective duly
authorized officers or representatives have set their hands hereunto effective
upon the date first above written.

COMPANY:                                   PENN OCTANE:

RIO VISTA GP LLC                           PENN OCTANE CORPORATION
a Delaware limited liability company       a Delaware corporation

By:
   -------------------------------
       Richard Shore, Jr.                By:
       President                            ------------------------------------
                                                 Jerome B. Richter
820 Gessner Road                                 Chief Executive Officer
Suite 1250
Houston, Texas  77024                    THE MEMBERS:

                                         SHORE CAPITAL LLC

                                         By:
                                            ------------------------------------
                                                 Richard Shore, Jr., President

                                            ------------------------------------
                                            Jerome B. Richter

                      [Signature Page to Voting Agreement]

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