Document:

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                                                                    EXHIBIT 10.1

                CONTRIBUTION, CONVEYANCE AND ASSUMPTION AGREEMENT

         This Contribution, Conveyance and Assumption Agreement (this
"Agreement") dated effective as of ______________, 2003, is entered into by and
among Penn Octane Corporation, a Delaware corporation ("POCC"), Rio Vista GP
LLC, a Delaware limited liability company (the "GP"), Rio Vista Energy Partners
L.P., a Delaware limited partnership (the "MLP"), Rio Vista Operating GP LLC, a
Delaware limited liability company (the "Operating GP"), and Rio Vista Operating
Partnership L.P., a Delaware limited partnership (the "Operating Partnership").

                                    RECITALS

         WHEREAS, prior to the date hereof, POCC formed the GP, as a
wholly-owned direct subsidiary, and purchased for $1,000.00 all of the limited
liability company interests in the GP;

         WHEREAS, the GP and POCC formed the MLP, with the GP purchasing a 2%
general partner interest for $20 and POCC purchasing common units representing a
98% limited partner interest for $980.00;

         WHEREAS, the MLP formed the Operating GP and purchased all of the
limited liability company interests in the Operating GP for $1,000.00;

         WHEREAS, POCC and the Operating GP formed the Operating Partnership,
with the Operating GP purchasing a 0.10% general partner interest for $1.00 and
POCC purchasing a 99.9% limited partner interest for $999.00;

         WHEREAS, each of the following transactions shall occur as of 12:01
A.M. Eastern Time on ________, 2003 (the "Contribution Effective Time"):

         1. POCC will contribute all of the outstanding capital stock of its
subsidiaries (the "Subsidiary Interests") set forth on Exhibit A (the
"Subsidiaries") hereto to the Operating Partnership as a capital contribution;

         2. POCC will contribute to the Operating Partnership the assets set
forth in the Conveyance Agreement described in Section 1.2 below (the "LPG
Assets") as an additional capital contribution; and

         3. The GP will convey $1,000 to the MLP in exchange for the issuance of
incentive distribution rights to the GP;

         WHEREAS, each of the following transactions shall occur as of 12:02
A.M. Eastern Time on ___________, 2003 (the "Closing Day Effective Time"):

         1. POCC will contribute all of its limited partner interest in the
Operating Partnership to the MLP as an additional capital contribution.

         NOW, THEREFORE, in consideration of their mutual undertakings and
agreements hereunder, the parties to this Agreement undertake and agree as
follows:

                                    ARTICLE I

         CONVERSIONS, CONTRIBUTIONS AND DISTRIBUTIONS OF VARIOUS ASSETS

         SECTION 1.1 CONTRIBUTION OF THE SUBSIDIARY INTERESTS BY POCC TO THE
OPERATING PARTNERSHIP. At the Contribution Effective Time, POCC hereby grants,
contributes, transfers, assigns and conveys to the Operating Partnership, its
successors and assigns, all right, title and interest in and to the Subsidiary
Interests as a capital contribution and the Operating Partnership hereby accepts
the Subsidiary Interests.

<PAGE>

         SECTION 1.2 CONTRIBUTION OF LPG ASSETS BY POCC TO THE OPERATING
PARTNERSHIP. At the Contribution Effective Time, POCC hereby grants,
contributes, transfers, assigns and conveys to the Operating Partnership, its
successors and assigns, all right, title and interest in and to the LPG Assets,
and the Operating Partnership hereby accepts the LPG Assets. In order to give
full effect to the foregoing grant, contribution, transfer, assignment and
conveyance, POCC, as grantor, and the Operating Partnership, as grantee, shall
execute a Conveyance Agreement in the form attached hereto as Exhibit B together
with such other special warranty deeds, conveyances or other documents required
to transfer the LPG Assets in the jurisdictions in which they are located.

         SECTION 1.3 CONTRIBUTION OF OPERATING PARTNERSHIP INTEREST BY POCC TO
THE MLP. At the Closing Day Effective Time, POCC hereby grants, contributes,
transfers, assigns and conveys to the MLP, its successors and assigns, all
right, title and interest of POCC in and to the 99.9% limited partner interest
in the Operating Partnership as an additional capital contribution to the MLP
and the Operating Partnership hereby accepts such limited partner interest as an
additional capital contribution to the Operating Partnership.

         SECTION 1.4 CONVEYANCE BY THE GP TO THE MLP. At the Closing Day
Effective Time, the GP hereby conveys to the MLP $1,000.00 in exchange for all
of the incentive distribution rights under the First Amended and Restated
Agreement of Limited Partnership of the MLP.

                                   ARTICLE II

                 RECORDATION OF EVIDENCE OF OWNERSHIP OF ASSETS

         SECTION 2.1. In connection with the conveyances that are referred to in
Article I to this Agreement, the parties to this Agreement acknowledge that
certain jurisdictions in which the assets of the applicable parties to such
conveyances are located may require that documents be recorded by such parties
resulting from such conveyances in order to evidence title to the assets owned
by such parties. All such documents shall evidence such new ownership and are
not intended to modify, and shall not modify, any of the terms, covenants and
conditions herein set forth.

                                   ARTICLE III

                        ASSUMPTION OF CERTAIN LIABILITIES

         SECTION 3.1 ASSUMPTION OF LIABILITIES AND OBLIGATIONS BY THE OPERATING
PARTNERSHIP AND THE MLP. In connection with the contributions of the LPG Assets
and the Subsidiary Interests to the Operating Partnership, the Operating
Partnership hereby assumes and agrees to duly and timely pay, perform and
discharge all obligations and liabilities associated with the Contributed
Assets, that arise from and after the date of this Agreement, to the full extent
that either of the Subsidiaries or POCC would have been obligated to pay,
perform and discharge such obligations and liabilities in the future, were it
not for the execution and delivery of this Agreement; provided, however, that
said assumption and agreement to duly and timely pay, perform and discharge such
obligations and liabilities shall not increase the obligation of the Operating
Partnership with respect to such obligations and liabilities beyond that of POCC
as to the LPG Assets, or the Subsidiaries as to the assets acquired by the
Operating Partnership in such interest conveyed by any of POCC or the
Subsidiaries. For purposes of this Agreement, the term "Contributed Assets"
shall mean, collectively, the LPG Assets and the Subsidiary Interests.

                                       2
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                                   ARTICLE IV

                                  TITLE MATTERS

SECTION 4.1       DISCLAIMER OF WARRANTIES; SUBROGATION.

(a)      (i) NOTWITHSTANDING ANYTHING TO THE CONTRARY CONTAINED IN THIS
         AGREEMENT, THE MLP AND THE OPERATING PARTNERSHIP ACKNOWLEDGE AND AGREE
         THAT POCC AND THE SUBSIDIARIES HAVE NOT MADE, DO NOT MAKE, AND
         SPECIFICALLY NEGATE AND DISCLAIM, ANY REPRESENTATIONS, WARRANTIES,
         PROMISES, COVENANTS, AGREEMENTS OR GUARANTIES OF ANY KIND OR CHARACTER
         WHATSOEVER, WHETHER EXPRESS, IMPLIED OR STATUTORY, ORAL OR WRITTEN,
         PAST OR PRESENT (ALL OF WHICH ARE EXPRESSLY DISCLAIMED BY POCC AND THE
         SUBSIDIARIES) REGARDING (1) THE TITLE, VALUE, NATURE, QUALITY OR
         CONDITION OF THE CONTRIBUTED ASSETS, (2) THE INCOME TO BE DERIVED FROM
         THE CONTRIBUTED ASSETS, (3) THE SUITABILITY OF THE CONTRIBUTED ASSETS
         FOR ANY AND ALL ACTIVITIES AND USES WHICH THE MLP MAY CONDUCT THEREON,
         (4) THE COMPLIANCE OF OR BY THE CONTRIBUTED ASSETS, OR THEIR OPERATIONS
         WITH ANY LAWS (INCLUDING WITHOUT LIMITATION ANY ZONING, ENVIRONMENTAL
         PROTECTION, POLLUTION OR LAND USE LAWS, RULES, REGULATIONS, ORDERS OR
         REQUIREMENTS), OR (5) THE HABITABILITY, MERCHANTABILITY, MARKETABILITY,
         PROFITABILITY OR FITNESS FOR A PARTICULAR PURPOSE OF THE CONTRIBUTED
         ASSETS.

(ii)     THE MLP AND THE OPERATING PARTNERSHIP ACKNOWLEDGE AND AGREE THAT THEY
         HAVE HAD THE OPPORTUNITY TO INSPECT THE CONTRIBUTED ASSETS, AND THAT
         THEY ARE RELYING SOLELY ON THEIR OWN INVESTIGATION OF THE CONTRIBUTED
         ASSETS, AND NOT ON ANY INFORMATION PROVIDED OR TO BE PROVIDED BY POCC
         AND THE SUBSIDIARIES, AND POCC AND THE SUBSIDIARIES ARE NOT LIABLE OR
         BOUND IN ANY MANNER BY ANY VERBAL OR WRITTEN STATEMENTS,
         REPRESENTATIONS OR INFORMATION PERTAINING TO THE CONTRIBUTED ASSETS,
         FURNISHED BY ANY AGENT, EMPLOYEE, SERVANT OR THIRD PARTY.

(iii)    THE MLP AND THE OPERATING PARTNERSHIP ACKNOWLEDGE THAT TO THE MAXIMUM
         EXTENT PERMITTED BY LAW, THE CONTRIBUTION OF THE CONTRIBUTED ASSETS, AS
         PROVIDED FOR HEREIN IS MADE ON AN "AS IS", "WHERE IS" BASIS WITH ALL
         FAULTS AND THE CONTRIBUTED ASSETS, ARE CONTRIBUTED OR DISTRIBUTED AND
         CONVEYED BY POCC AND THE SUBSIDIARIES SUBJECT TO THE FOREGOING. THIS
         PARAGRAPH SHALL SURVIVE SUCH CONTRIBUTION OR DISTRIBUTION AND
         CONVEYANCE OR THE TERMINATION OF THIS AGREEMENT.

(iv)     THE PROVISIONS OF THIS SECTION 4.1 HAVE BEEN NEGOTIATED BY POCC, THE
         SUBSIDIARIES, THE MLP AND THE OPERATING PARTNERSHIP AFTER DUE
         CONSIDERATION AND ARE INTENDED TO BE A COMPLETE EXCLUSION AND NEGATION
         OF ANY REPRESENTATIONS OR WARRANTIES OF POCC AND THE SUBSIDIARIES,
         WHETHER EXPRESS, IMPLIED OR STATUTORY, WITH RESPECT TO THE CONTRIBUTED
         ASSETS, THAT MAY ARISE PURSUANT TO ANY LAW NOW OR HEREAFTER IN EFFECT,
         OR OTHERWISE.

(b)      The contributions of the Contributed Assets, made under this Agreement
         are made with full rights of substitution and subrogation of the
         Operating Partnership, and all persons claiming by, through and under
         the Operating Partnership, to the extent assignable, in and to all
         covenants and warranties by the predecessors-in-title of POCC and the
         Subsidiaries, and with full subrogation of all rights accruing under
         applicable statutes of limitation and all rights of action of warranty

                                       3
<PAGE>

         against all former owners of the Contributed Assets.

(c)      POCC, the Subsidiaries, the MLP, the GP, the Operating Partnership and
         Operating GP agree that the disclaimers contained in this Section 4.1
         are "conspicuous" disclaimers. Any covenants implied by statute or law
         by the use of the words "grant," "convey," "bargain," "sell," "assign,"
         "transfer," "deliver," or "set over" or any of them or any other words
         used in this Agreement or any exhibits hereto are hereby expressly
         disclaimed, waived or negated.

                                   ARTICLE V

                               FURTHER ASSURANCES

         SECTION 5.1 FURTHER ASSURANCES. From time to time after the date
hereof, and without any further consideration, POCC, the Subsidiaries, the GP,
the MLP, the Operating GP and the Operating Partnership shall execute,
acknowledge and deliver all such additional deeds, assignments, conveyances,
instruments, notices, releases, acquittances and other documents, and will do
all such other acts and things, all in accordance with applicable law, as may be
necessary or appropriate more fully and effectively to vest in the Operating
Partnership and the MLP and their successors and assigns beneficial and record
title to the Contributed Assets hereby contributed and assigned to the Operating
Partnership or intended so to be and to more fully and effectively carry out the
purposes and intent of this Agreement.

         SECTION 5.2 OTHER ASSURANCES. From time to time after the date hereof,
and without any further consideration, each of the parties to this Agreement
shall execute, acknowledge and deliver all such additional instruments, notices
and other documents, and will do all such other acts and things, all in
accordance with applicable law, as may be necessary or appropriate to more fully
and effectively carry out the purposes and intent of this Agreement.

                                   ARTICLE VI

                                  MISCELLANEOUS

         SECTION 6.1 HEADINGS; REFERENCES; INTERPRETATION. All article and
section headings in this Agreement are for convenience only and shall not be
deemed to control or affect the meaning or construction of any of the provisions
hereof. The words "hereof," "herein" and "hereunder" and words of similar
import, when used in this Agreement, shall refer to this Agreement as a whole,
including without limitation, all exhibits attached hereto, and not to any
particular provision of this Agreement. All references herein to articles,
sections, and exhibits shall, unless the context requires a different
construction, be deemed to be references to the articles, sections and exhibits
of this Agreement, respectively, and all such Exhibits attached hereto are
hereby incorporated herein and made a part hereof for all purposes. All personal
pronouns used in this Agreement, whether used in the masculine, feminine or
neuter gender, shall include all other genders, and the singular shall include
the plural and vice versa. The use herein of the word "including" following any
general statement, term or matter shall not be construed to limit such
statement, term or matter to the specific items or matters set forth immediately
following such word or to similar items or matters, whether or not non-limiting
language (such as "without limitation," "but not limited to," or words of
similar import) is used with reference thereto, but rather shall be deemed to
refer to all other items or matters that could reasonably fall within the
broadest possible scope of such general statement, term or matter.

         SECTION 6.2 SUCCESSORS AND ASSIGNS. This Agreement shall be binding
upon and inure to the benefit of the parties signatory hereto and their
respective successors and assigns.

         SECTION 6.3 NO THIRD PARTY RIGHTS. The provisions of this Agreement are
intended to bind the parties signatory hereto as to each other and are not
intended to and do not create rights in any other person or confer upon any
other person any benefits, rights or remedies and no person is or is intended to
be a third party beneficiary of any of the provisions of this Agreement.

                                       4
<PAGE>

         SECTION 6.4 COUNTERPARTS. This Agreement may be executed in any number
of counterparts, all of which together shall constitute one agreement binding on
the parties hereto.

         SECTION 6.5 GOVERNING LAW. This Agreement shall be governed by, and
construed in accordance with, the laws of the State of Texas applicable to
contracts made and to be performed wholly within such state without giving
effect to conflict of law principles thereof, except to the extent that it is
mandatory that the law of some other jurisdiction, shall apply.

         SECTION 6.6 SEVERABILITY. If any of the provisions of this Agreement
are held by any court of competent jurisdiction to contravene, or to be invalid
under, the laws of any political body having jurisdiction over the subject
matter hereof, such contravention or invalidity shall not invalidate the entire
Agreement. Instead, this Agreement shall be construed as if it did not contain
the particular provision or provisions held to be invalid, and an equitable
adjustment shall be made and necessary provision added so as to give effect to
the intention of the parties as expressed in this Agreement at the time of
execution of this Agreement.

         SECTION 6.7 AMENDMENT OR MODIFICATION. This Agreement may be amended or
modified from time to time only by the written agreement of all the parties
hereto.

         SECTION 6.8 INTEGRATION. This Agreement, together with that certain
Omnibus Agreement dated of even date herewith, to be entered into by and among
POCC, certain of POCC's subsidiaries, the MLP, the GP, the Operating Partnership
and the Operating GP (the "Omnibus Agreement"), supersedes all previous
understandings or agreements between the parties, whether oral or written, with
respect to its subject matter. This document is an integrated agreement which
contains the entire understanding of the parties. No understanding,
representation, promise or agreement, whether oral or written, other than those
contained in the Omnibus Agreement, is intended to be or shall be included in or
form part of this Agreement unless it is contained in a written amendment hereto
executed by the parties hereto after the date of this Agreement.

                         (Signatures on following page)

                                       5
<PAGE>

         IN WITNESS WHEREOF, this Agreement has been duly executed by the
parties hereto as of the date first above written.

                           PENN OCTANE CORPORATION

                           By:________________________________________
                           Name:______________________________________
                           Title:_____________________________________

                           RIO VISTA GP LLC

                           By:________________________________________
                           Name:______________________________________
                           Title:_____________________________________

                           RIO VISTA ENERGY PARTNERS L.P.

                           By: RIO VISTA GP LLC,
                               its General Partner

                               By:____________________________________
                               Name:__________________________________
                               Title:_________________________________

                           RIO VISTA OPERATING GP LLC

                           By:________________________________________
                           Name:______________________________________
                           Title:_____________________________________

                           RIO VISTA OPERATING PARTNERSHIP L.P.

                           By: Rio Vista Operating GP LLC, its General Partner

                               By: Rio Vista Energy Partners L.P.,
                                   its sole member

                                   By: Rio Vista GP LLC,
                                       its General Partner

                                       By:____________________________________
                                       Name:__________________________________
                                       Title:_________________________________

                                           6
<PAGE>

                                    EXHIBIT A

                              LIST OF SUBSIDIARIES

         Penn-Octane de Mexico, S.A. de C.V.

         Termatsal, S.A. de C.V.

<PAGE>

                                    EXHIBIT B

<PAGE>

                              CONVEYANCE AGREEMENT

         Recording Requested by and When Recorded Return to: Fulbright &
Jaworski L.L.P., 300 Convent St., Suite 2200, San Antonio, Texas, Attn:
Christian G. Herff.

                              CONVEYANCE AGREEMENT

         This Conveyance Agreement (this "Conveyance"), effective as of 12:01
A.M. Eastern Time on ________________, 2003 (the "Effective Date"), is from PENN
OCTANE CORPORATION, a Delaware corporation (herein called "Grantor"), and in
favor of RIO VISTA OPERATING PARTNERSHIP L.P., whose mailing address is 77-530
Enfield Lane, Building D, Palm Desert, CA 92211 (herein called "Grantee").

                                    ARTICLE I

                                 GRANTING CLAUSE

         1.1 GRANTING CLAUSES. Grantor hereby contributes, conveys, assigns,
transfers, delivers, and sets over unto Grantee, its successors and assigns, all
right, title, interests and estate of Grantor in and to the following described
property, to-wit:

         ALL OF THE ASSETS SET FORTH ON SCHEDULE A ATTACHED HERETO

         The property described in this Section 1.1 shall be referred to herein
collectively as the "Subject Property".

         TO HAVE AND TO HOLD the Subject Property, subject to the terms and
conditions hereof, unto Grantee, its successors and assigns, forever.

                                   ARTICLE II

                      ENCUMBRANCES AND WARRANTY DISCLAIMERS

         2.1 PERMITTED ENCUMBRANCES. This Conveyance is made and accepted
expressly subject to (a) all liens, charges, encumbrances, contracts,
agreements, instruments, obligations, defects, restrictions, security interests,
options or preferential rights to purchase, adverse claims, reservations,
exceptions, easements, rights-of-way, conditions, leases, other matters
affecting the Subject Property or to which it is subject; and (b) to all matters
that a current on the ground survey or visual inspection would reflect.

         2.2 CONTRIBUTION AGREEMENT. This Conveyance is expressly made subject
to the terms and conditions of that certain Contribution, Conveyance and
Assumption Agreement dated as of _____________, 2003, among Grantor, Grantee and
the other parties thereto (the "Contribution Agreement"). All capitalized terms
used herein shall have the meanings given to such terms in the Contribution
Agreement, unless otherwise defined herein. Nothing contained in this Conveyance
shall in any way affect the provisions set forth in the Contribution Agreement
nor shall this Conveyance expand or contract any rights or remedies under the
Contribution Agreement. This Conveyance is intended only to effect the transfer
of the Subject Property to Grantee as provided for in the Contribution Agreement
and shall be governed entirely in accordance with the terms and conditions of
the Contribution Agreement. In the event of a conflict between the terms of this
Conveyance and the terms of the Contribution Agreement, the terms of the
Contribution Agreement shall prevail.

         2.3 DISCLAIMER OF WARRANTIES; SUBROGATION. Except as expressly provided
herein or in the Contribution Agreement, this Conveyance is made, and is
accepted by Grantee, without warranty of title, express, implied or statutory,
and without recourse, but with full substitution and subrogation of Grantee, and
all persons claiming by, through, and under Grantee, to the extent assignable,
in and to all covenants and warranties by the predecessors in title of Grantor
and with full subrogation of all rights accruing under applicable statutes of
limitation or prescription and all rights of action of warranty against all
former owners of the Subject Property. Except as expressly provided herein or in
the Contribution Agreement, any covenants implied by statute or by the

                                      D-1
<PAGE>

use of the words "convey", "sell", "assign", "transfer", "deliver", or "set
over" or any of them or any other words used in this Conveyance, are hereby
expressly disclaimed, waived and negated.

                                   ARTICLE III

                                  MISCELLANEOUS

         3.1 FURTHER ASSURANCES. Grantor and Grantee agree to take all such
further actions and to execute, acknowledge and deliver all such further
documents that are necessary or useful in carrying out the purposes of this
Conveyance. So long as authorized by applicable law so to do, Grantor agrees to
execute, acknowledge and deliver to Grantee all such other additional
instruments, notices, affidavits, deeds, conveyances, assignments and other
documents and to do all such other and further acts and things as may be
necessary or useful to more fully and effectively grant, assign, convey,
transfer and deliver to Grantee the Subject Property conveyed hereby or intended
so to be conveyed.

         3.2 SUCCESSORS AND ASSIGNS; NO THIRD PARTY BENEFICIARY. This Conveyance
shall be binding upon, and shall inure to the benefit of, Grantor and Grantee
and their successors and assigns. The provisions of this Conveyance are not
intended to and do not create rights in any other person or entity or confer
upon any other person or entity any benefits, rights or remedies and no person
or entity is or is intended to be a third party beneficiary of any of the
provisions of this Conveyance.

         3.3 GOVERNING LAW. This Conveyance and the legal relations between the
parties shall be governed by, and construed in accordance with, the laws of the
State of Texas, excluding any conflict of law rule which would refer any issue
to the laws of another jurisdiction, except when it is mandatory that the law of
the jurisdiction wherein the Subject Property is located shall apply.

         3.4 HEADINGS; REFERENCES; DEFINED TERMS. All Section headings in this
Conveyance are for convenience only and shall not be deemed to control or affect
the meaning or construction of any of the provisions hereof. The words "hereof",
"herein" and "hereunder" and words of similar import, when used in this
Conveyance, shall refer to this Conveyance as a whole, including, without
limitation, all Schedules and Exhibits attached hereto, and not to any
particular provision of this Conveyance.

         3.5 COUNTERPARTS. This Conveyance may be executed in any number of
counterparts, all of which together shall constitute one agreement binding on
the parties hereto.

         3.6 SEVERABILITY. If any of the provisions of this Conveyance are held
by any court of competent jurisdiction to contravene, or to be invalid under,
the laws of any political body having jurisdiction over the subject matter
hereof, such contravention or invalidity shall not invalidate the entire
agreement. Instead, this Conveyance shall be construed as if it did not contain
the particular provision or provisions held to be invalid and an equitable
adjustment shall be made and necessary provision added so as to give effect to
the intention of the parties as expressed in this Conveyance at the time of
execution of this Conveyance.

                                      D-2
<PAGE>

         IN WITNESS WHEREOF, this Conveyance has been duly executed by the
parties hereto on the dates of the acknowledgments set forth below, to be
effective, however, as of the Effective Date.

                           GRANTOR:

                           PENN OCTANE CORPORATION

                           By:____________________________________
                           Name:__________________________________
                           Title:_________________________________

                           GRANTEE:

                           RIO VISTA OPERATING PARTNERSHIP L.P.

                           By: Rio Vista Operating GP LLC, its General Partner

                               By: Rio Vista Energy Partners L.P.,
                                   its sole member

                                   By: Rio Vista GP LLC,
                                       its General Partner

                                       By:____________________________________
                                       Name:__________________________________
                                       Title:_________________________________

                                      D-3
<PAGE>

THE STATE OF TEXAS        )
                          )
COUNTY OF _________       )

         This instrument was acknowledged before me on the ____ day of ________,
2003, by ______________, ______________ of ______________________, on behalf of
and in [HIS/HER] capacity as __________ of ____________________.

                                  ____________________________________
                                  NOTARY PUBLIC

My Commission Expires: ________________

                                      D-4
<PAGE>

                                   SCHEDULE A

                                      D-5<PAGE>

                                                                    EXHIBIT 10.2

                                OMNIBUS AGREEMENT

                                     BETWEEN

                            PENN OCTANE CORPORATION,

                                RIO VISTA GP LLC,

                         RIO VISTA ENERGY PARTNERS L.P.

                                       AND

                      RIO VISTA OPERATING PARTNERSHIP L.P.

<PAGE>

                                OMNIBUS AGREEMENT

         THIS OMNIBUS AGREEMENT is entered into as of [______________], 2003 by
and among Penn Octane Corporation, a Delaware corporation ("POCC"), Rio Vista GP
LLC, a Delaware limited liability company (the "General Partner"), Rio Vista
Energy Partners L.P., a Delaware limited partnership (the "Partnership"), and
Rio Vista Operating Partnership L.P. (the "Operating Partnership"). The
above-named entities are sometimes referred to in this Agreement each as a
"Party" and collectively as the "Parties."

                                    RECITALS:

         WHEREAS, POCC and its Affiliates (as defined herein) formed the
Partnership, the General Partner and the Operating Partnership for the purpose
of conducting of the Business (as defined below);

         WHEREAS, certain assets and services used by POCC or its Affiliates in
the conduct of the Business prior to the formation of the Partnership were not
transferred to the Partnership;

         WHEREAS, the Parties desire to ensure the continued effective operation
of the Business, and the Parties recognize that the continued effective
operation of the Business requires that POCC provide certain management and
employee services to the Business as set forth in this Agreement; and

         WHEREAS, the Parties desire to evidence other agreements and
relationships, as more fully set out in this Agreement, with respect to the
transfer of the Business to the Partnership and the Operating Partnership as
well as the operation of the Business by the Partnership and the Operating
Partnership.

         NOW THEREFORE, in consideration of the premises and the covenants,
conditions, and agreements contained herein, and for other good and valuable
consideration, the receipt and sufficiency of which are hereby acknowledged, the
Parties hereto hereby agree as follows:

                                    ARTICLE I

                                   DEFINITIONS

         DEFINITIONS. (a) As used in this Agreement, the following terms shall
have the respective meanings set forth below:

         "Affiliate" means, with respect to any Person, any other Person that
directly or indirectly through one or more intermediaries controls, is
controlled by or is under common control with, the Person in question. As used
herein, the term "control" means the possession, direct or indirect, 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.

                                       2
<PAGE>

         "Agreement" means this Omnibus Agreement, as it may be amended,
modified, or supplemented from time to time in accordance with Section 4.7
hereof.

         "Assets" means the "Contributed Assets" as such term is defined in the
Contribution Agreement.

         "Business" means (i) providing transportation, terminalling and
distribution services for hydrocarbon products and by-products, and (ii)
marketing and selling hydrocarbon products and by-products.

         "Closing Date" means the date of the Distribution.

         "Conflicts Committee" is defined in the Partnership Agreement.

         "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.

         "Contribution Agreement" means the Contribution, Conveyance and
Assumption Agreement, dated [______________], 2003, by and among various POCC
Entities, the Partnership, the Operating Partnership, the General Partner and
Rio Vista Operating GP LLC, a Delaware limited liability company.

         "Covered Environmental Losses" is defined in Section 2.1(a).

         "Distribution" means the distribution by POCC of all the outstanding
common units of the Partnership representing limited partner interests to the
stockholders of POCC.

         "Environmental Laws" means all federal, state, and local laws,
statutes, rules, regulations, orders, and ordinances, now or hereafter in
effect, relating to protection of human health and the environment including,
without limitation, the federal Comprehensive Environmental Response,
Compensation, and Liability Act, the Superfund Amendments Reauthorization Act,
the Resource Conservation and Recovery Act, the Clean Air Act, the Federal Water
Pollution Control Act, the Toxic Substances Control Act, the Oil Pollution Act,
the Safe Drinking Water Act, the Hazardous Materials Transportation Act, and
other environmental conservation and protection laws, each as amended from time
to time.

         "General Partner" is defined in the introduction to this Agreement.

         "Hazardous Substance" means any substance that is designated, defined,
or classified as a hazardous waste, hazardous material, pollutant, contaminant,
or toxic or hazardous substance, or that is otherwise regulated under any
Environmental Law, including, without limitation, any hazardous substance as
defined under the Comprehensive Environmental Response, Compensation, and
Liability Act.

                                       3
<PAGE>

         "Indemnified Party" means the Partnership Entities or the POCC
Entities, as the case may be, in their capacity as the parties entitled to
indemnification in accordance with Article II.

         "Indemnifying Party" means either the Partnership Entities or the POCC
Entities, as the case may be, in its capacity as the parties from whom
indemnification may be sought in accordance with Article II.

         "Losses" means any losses, damages, liabilities, claims, demands,
causes of action, judgments, settlements, fines, penalties, costs, and expenses
(including, without limitation, court costs and reasonable attorney's and
expert's fees) of any and every kind or character.

         "POCC" is defined in the introduction to this Agreement.

         "POCC Entities" means POCC and each of its Subsidiaries (other than the
General Partner, the Partnership and any Subsidiary of the Partnership).

         "Partnership" is defined in the introduction to this Agreement.

         "Partnership Agreement" means the First Amended and Restated Agreement
of Limited Partnership of Rio Vista Energy Partners L.P., dated as of, and in
the form on, the Closing Date. No amendment or modification to the Partnership
Agreement subsequent to the Closing Date shall be given effect for the purposes
of this Agreement unless consented to by each of the Parties to this Agreement.

         "Partnership Entities" means the Partnership, the General Partner and
each Subsidiary of the Partnership.

         "Party" and "Parties" is defined in the introduction to this Agreement.

         "Pass-Through Environmental Losses" is defined in Section 2.1(b).

         "Person" means an individual or a corporation, limited liability
company, partnership, joint venture, trust, unincorporated organization,
association, government agency or political subdivision thereof or other entity.

         "Retained Assets" means, collectively, any assets and investments owned
by any of the POCC Group that were not conveyed, contributed or otherwise
transferred to any of the Partnership Entities prior to or on the Closing Date.

         "Services" is defined in Section 3.1.

         "Subsidiary" means, with respect to any Person, (a) a corporation of
which more than 50% of the voting power is owned, directly or indirectly, at the
date of determination, by such Person, by one or more Subsidiaries of such
Person or a combination thereof, (b) a partnership (whether general or limited)
in which such Person or a Subsidiary of such Person is, at the date of
determination, a general or limited partner of such partnership, but only if
more than 50% of

                                       4
<PAGE>

the partnership interests of such partnership (considering all of the
partnership interests of the partnership as a single class) is owned, directly
or indirectly, at the date of determination, by such Person, by one or more
Subsidiaries of such Person, or a combination thereof, or (c) any other Person
(other than a corporation or a partnership) in which such Person, one or more
Subsidiaries of such Person, or a combination thereof, directly or indirectly,
at the date of determination, has (i) at least a majority ownership interest or
(ii) the power to elect or direct the election of a majority of the directors or
other governing body of such Person.

                                   ARTICLE II

                                 INDEMNIFICATION

         2.1      ENVIRONMENTAL INDEMNIFICATION.

                  (a)      Subject to the limitations contained in this Section
2.1(a), POCC shall indemnify, defend and hold harmless each of the Partnership
Entities from and against environmental and toxic tort Losses suffered, incurred
or paid by any of the Partnership Entities by reason of or arising out of:

                           (i)      any violation or correction of violation of
Environmental Laws associated with the Assets or the Retained Assets, or

                           (ii)     any event or condition associated with the
ownership or operation of the Assets or the Retained Assets (including, without
limitation, the presence of Hazardous Substances on, under, about or migrating
to or from the Assets or the Retained Assets or the disposal or release of
Hazardous Substances generated by operation of the Assets or the Retained Assets
at non-Asset locations) including, without limitation, (A) the cost and expense
of any investigation, assessment, evaluation, monitoring, containment, cleanup,
repair, restoration, remediation, or other corrective action required or
necessary under Environmental Laws, (B) the cost or expense of the preparation
and implementation of any closure, remedial, corrective action, or other plans
required or necessary under Environmental Laws, and (C) the cost and expense for
any environmental or toxic tort pre-trial, trial, or appellate legal or
litigation support work,

but only to the extent that such violation complained of under Section 2.1(a)(i)
or such events or conditions included under Section 2.1(a)(ii) occurred before
the Closing Date (collectively, "Covered Environmental Losses").

                  (b)      POCC shall indemnify, defend and hold harmless any of
the Partnership Entities from and against any Losses suffered or incurred by any
of the Partnership Entities to the extent that POCC is entitled to and receives
indemnification, is defended or held harmless against any such Losses from any
third-party pursuant to any agreement between any third-party and POCC
(collectively, "Pass-Through Environmental Losses"). In furtherance of such
agreement, POCC agrees to use its best commercially reasonable efforts to
pursue, for the benefit of the Partnership Entities, any such indemnification
with respect to which it might be entitled if

                                       5
<PAGE>

requested by the Partnership; provided that, the Partnership shall reimburse
POCC for all costs and expenses incurred in connection with pursuing such
indemnity on behalf of the Partnership.

                  (c)      The Partnership shall indemnify, defend and hold
harmless POCC from and against Losses suffered or incurred by any of the POCC
Entities by reason of or arising out of:

                           (i)      any violation or correction of violation of
Environmental Laws associated with the Assets, or

                           (ii)     any event or condition associated with
ownership or operation of the Assets (including, but not limited to, the
presence of Hazardous Substances on, under, about or migrating to or from the
Assets or the disposal or release of Hazardous Substances generated by operation
of the Assets at non-Asset locations) including, without limitation, (A) the
cost and expense of any investigation, assessment, evaluation, monitoring,
containment, cleanup, repair, restoration, remediation, or other corrective
action required or necessary under Environmental Laws, (B) the cost or expense
of the preparation and implementation of any closure, remedial, corrective
action, or other plans required or necessary under Environmental Laws, and (C)
the cost and expense for any environmental or toxic tort pre-trial, trial, or
appellate legal or litigation support work,

but only to the extent such violation complained of under Section 2.1(c)(i) or
such events or conditions included under Section 2.1(c)(ii) occurred after the
Closing Date.

         2.2      ADDITIONAL INDEMNIFICATION

                  (a)      In addition to and not in limitation of the
indemnification provided under Sections 2.1(a) and 2.1(b), POCC shall indemnify,
defend, and hold harmless the Partnership Entities from and against any Losses
suffered or incurred by the Partnership Entities by reason of or arising out of

                           (i)      any events and conditions associated with
the ownership or operation of the Retained Assets, whether occurring before or
after the Closing Date,

                           (ii)     the failure of the Partnership Entities to
be the owner of such valid leasehold interests or fee ownership interests in and
to the Assets as are necessary to enable the Partnership Entities to continue to
own and operate the Assets and the Business in the same manner that the Assets
and the Business were owned and operated by the POCC Entities during the
one-year period immediately prior to the Closing Date to the extent that POCC is
notified of any of the foregoing within three years after the Closing Date,

                           (iii)    the failure of the Partnership Entities to
have any consent or permit necessary to allow the Partnership Entities to own or
operate the Assets and the Business in the same manner that the Assets and the
Business were owned and operated by the POCC Entities

                                       6
<PAGE>

during the one-year period immediately prior to the Closing Date to the extent
that POCC is notified of any of the foregoing within three years after the
Closing Date,

                           (iv)     all legal actions against POCC, including
without limitation, those set forth on Schedule 2.2 hereto, and

                           (v)      all federal, state and local income tax
liabilities attributable to the operation of the Assets prior to the Closing
Date.

                  (b)      In addition to and not in limitation of the
indemnification provided under Sections 2.1(c), or under the Partnership
Agreement, the Partnership shall indemnify, defend, and hold harmless the POCC
Entities from and against any Losses suffered or incurred by any of the POCC
Entities by reason of or arising out of events and conditions associated with:

                                    (i)      the operation of the Assets and the
Business,

                                    (ii)     the performance of the Services by
POCC and/or its employees pursuant to this Agreement (provided that POCC is not
in breach of this Agreement), in each case occurring on or after the Closing
Date (other than Covered Environmental Losses which are provided for under
Section 2.1), unless in any such case such indemnification would not be
permitted under Section 7.7 of the Partnership Agreement, and

                  (c)      In addition to and not in limitation of the
indemnification provided under Sections 2.1(c) and 2.2(b), or under the
Partnership Agreement, the Partnership shall indemnify, for a period of three
years from the fiscal year end that includes the Closing Date, the POCC Entities
for federal income tax liabilities, including penalties and interest, resulting
from the Distribution and restructuring transactions connected with it to the
extent such federal income tax liabilities exceed $2.5 million in the aggregate.

         2.3      INDEMNIFICATION PROCEDURES.

                  (a)      The Indemnified Party agrees that within a reasonable
period of time after it becomes aware of facts giving rise to a claim for
indemnification under this Article II, it will provide notice thereof in writing
to the Indemnifying Party, specifying the nature of and specific basis for such
claim.

                  (b)      The Indemnifying Party shall have the right to
control all aspects of the defense of (and any counterclaims with respect to)
any claims brought against the Indemnified Party that are covered by the
indemnification under this Article II, including, without limitation, the
selection of counsel, determination of whether to appeal any decision of any
court and the settling of any such matter or any issues relating thereto;
provided however, that no such settlement shall be entered into without the
consent of the Indemnified Party unless it includes a full release of the
Indemnified Party from such matter or issues, as the case may be.

                                       7
<PAGE>

                  (c)      The Indemnified Party agrees to cooperate fully with
the Indemnifying Party, with respect to all aspects of the defense of any claims
covered by the indemnification under this Article II, including, without
limitation, the prompt furnishing to the Indemnifying Party of any
correspondence or other notice relating thereto that the Indemnified Party may
receive, permitting the name of the Indemnified Party to be utilized in
connection with such defense, the making available to the Indemnifying Party of
any files, records or other information of the Indemnified Party that the
Indemnifying Party considers relevant to such defense and the making available
to the Indemnifying Party of any employees of the Indemnified Party; provided
however, that in connection therewith the Indemnifying Party agrees to use
reasonable efforts to minimize the impact thereof on the operations of the
Indemnified Party. In no event shall the obligation of the Indemnified Party to
cooperate with the Indemnifying Party as set forth in the immediately preceding
sentence be construed as imposing upon the Indemnified Party an obligation to
hire and pay for counsel in connection with the defense of any claims covered by
the indemnification set forth in this Article II; provided however, that the
Indemnified Party may, at its own option, cost and expense, hire and pay for
counsel in connection with any such defense. The Indemnifying Party agrees to
keep any such counsel hired by the Indemnified Party reasonably informed as to
the status of any such defense, but the Indemnifying Party shall have the right
to retain sole control over such defense.

                  (d)      In determining the amount of any Losses for which the
Indemnified Party is entitled to indemnification under this Agreement, the gross
amount of the indemnification will be reduced by (i) any insurance proceeds
realized or to be realized by the Indemnified Party, and such correlative
insurance benefit shall be net of any incremental insurance premium that becomes
due and payable by the Indemnified Party as a result of such claim and (ii) all
amounts recovered or recoverable by the Indemnified Party under contractual
indemnities from third parties.

                                       8
<PAGE>

                                  ARTICLE III

                     SERVICES AND RELATED PARTY TRANSACTIONS

         3.1 SERVICES. During the term of this Agreement, POCC agrees to provide
(either directly or through its Subsidiaries) on behalf of the General Partner
in accordance with Article VII of the Partnership Agreement, the employees or
independent contractors, corporate staff, support services and administrative
services necessary to operate the Business (the "Services"). POCC shall perform
the Services in a manner that is substantially identical in nature and quality
to the services performed by POCC for the Business during the one-year period
immediately prior to the Closing Date. The General Partner and the Partnership
agree that POCC shall be reimbursed for all costs and expenses incurred in
connection with the performance of the Services as if it were the General
Partner in accordance with Section 7.4(b) and 7.6(c) of the Partnership
Agreement.

         3.2 DESIGNATION OF AGENTS. In connection with the provision of the
Services by the employees of POCC, the General Partner, on behalf of the
Partnership, hereby appoints and empowers POCC and each current and future
employee of POCC who is fulfilling a job function for the Partnership in
connection with the conduct by the Partnership of its business in the ordinary
course, as agent of the Partnership with full power and authority to execute and
deliver on behalf of the Partnership, any documents, contracts, governmental
filings or other instruments commensurate with, but limited to, such job
function. The power and authority granted pursuant to this Section 3.2 to a
person described in the preceding sentence will be valid only for so long as
such person is employed by POCC.

         3.3 RIGHT TO OPERATE. POCC shall have the right, but not the
obligation, to act as operator of the Partnership's facilities to the same
extent it acted as operator of such facilities prior to the effective date of
this Agreement for so long as POCC has responsibilities associated with such
facilities.

         3.4 RELATED PARTY TRANSACTIONS. Each of POCC, the General Partner, the
Partnership and the Operating Partnership agree that the execution or material
amendment of any "significant agreement" (as such term is defined below) must be
approved by the Conflicts Committee. The term "significant agreement" means any
agreement between the General Partner, the Partnership or the Operating
Partnership, on the one hand, and any POCC Entity, on the other hand, that
requires aggregate annual payments to or from any POCC Entity or POCC Entities
in excess of $100,000.

         3.5 BREACH BY PENN OCTANE. In the event POCC fails to perform the
Services as provided in Section 3.1 and does not cure such failure within ten
(10) days of receiving written notice of same from the General Partner, the
Partnership, in addition to any other remedies at law or in equity, may
terminate this Agreement and engage a third party for the provision of the
Services. POCC shall cooperate in good faith with the Partnership and the
General Partner in transitioning the Services to any such third party.

                                       9
<PAGE>

                                   ARTICLE IV

                                  MISCELLANEOUS

         4.1 INSURANCE MATTERS. POCC hereby agrees to cause each of the
Partnership Entities to be named as additional insureds in POCC's current
insurance program, which is described on Schedule 4.1 attached hereto. Each of
the Partnership Entities shall pay for its allocated cost of that insurance
coverage in an amount equal to POCC's cost of insuring the assets and operations
of Partnership Entity and generally in accordance with the allocations and
methodology described in Schedule 4.1.

         4.2 CHOICE OF LAW; SUBMISSION TO JURISDICTION. This Agreement shall be
subject to and governed by the laws of the State of Texas, excluding any
conflicts-of-law rule or principle that might refer the construction or
interpretation of this Agreement to the laws of another state. Each Party hereby
submits to the jurisdiction of the state and federal courts in Harris County,
Texas.

         4.3 NOTICE. All notices or requests or consents provided for by, or
permitted to be given pursuant to, this Agreement must be in writing and must be
given by depositing same in the United States mail, addressed to the Person to
be notified, postpaid, and registered or certified with return receipt requested
or by delivering such notice in person or by telecopier or telegram to such
Person. Notice given by personal delivery or mail shall be effective upon actual
receipt. Notice given by telegram or telecopier shall be effective upon actual
receipt if received during the recipient's normal business hours, or at the
beginning of the recipient's next business day after receipt if not received
during the recipient's normal business hours. All notices to be sent to a Party
pursuant to this Agreement shall be sent to or made at the address set forth
below such Party's signature to this Agreement, or at such other address as such
Party may stipulate to the other parties in the manner provided in this Section
4.3.

         4.4 ENTIRE AGREEMENT. This Agreement constitutes the entire agreement
of the Parties relating to the matters contained herein, superseding all prior
contracts or agreements, whether oral or written, relating to the matters
contained herein.

         4.5 TERMINATION. Unless earlier terminated as provided in this Section
4.5, the term of this Agreement shall be five (5) years from the date hereof and
shall be automatically renewed for subsequent five (5) year terms, unless and
until either party provides written notice to the other party at least sixty
(60) days prior to the expiration of the initial five (5) year term or any
renewal term that such party does not wish to renew this Agreement on the
expiration of the then current term. This Agreement, other than the provisions
of Article II, shall terminate on the earlier to occur of (i) ninety (90) days
after either party notifies the other party in writing that the Partnership is
no longer an Affiliate of POCC and (ii) this Agreement is terminated by the
Partnership under Section 3.5. Termination of this Agreement shall not terminate
any Indemnifying Party's continuing obligation of indemnification pursuant to
Article II of this Agreement which obligations shall survive as provided in
Article II.

                                       10
<PAGE>

         4.6 EFFECT OF WAIVER OR CONSENT. No waiver or consent, express or
implied, by any Party to or of any breach or default by any Person in the
performance by such Person of its obligations hereunder shall be deemed or
construed to be a consent or waiver to or of any other breach or default in the
performance by such Person of the same or any other obligations of such Person
hereunder. Failure on the part of a Party to complain of any act of any Person
or to declare any Person in default, irrespective of how long such failure
continues, shall not constitute a waiver by such Party of its rights hereunder
until the applicable statute of limitations period has run.

         4.7 AMENDMENT OR MODIFICATION. This Agreement may be amended or
modified from time to time only by the written agreement of all the Parties
hereto; provided however, that the Partnership may not, without the prior
approval of the Conflicts Committee, agree to any amendment or modification of
this Agreement. Each such instrument shall be reduced to writing and shall be
designated on its face an "Amendment" or an "Addendum" to this Agreement.

         4.8 ASSIGNMENT. No Party shall have the right to assign its rights or
obligations under this Agreement without the consent of the other Parties
hereto.

         4.9 COUNTERPARTS. This Agreement may be executed in any number of
counterparts with the same effect as if all signatory parties had signed the
same document. All counterparts shall be construed together and shall constitute
one and the same instrument.

         4.10 SEVERABILITY. If any provision of this Agreement or the
application thereof to any Person or circumstance shall be held invalid or
unenforceable to any extent, the remainder of this Agreement and the application
of such provision to other Persons or circumstances shall not be affected
thereby and shall be enforced to the greatest extent permitted by law.

         4.11 FURTHER ASSURANCES. In connection with this Agreement and all
transactions contemplated by this Agreement, each signatory party hereto agrees
to execute and deliver such additional documents and instruments and to perform
such additional acts as may be necessary or appropriate to effectuate, carry out
and perform all of the terms, provisions and conditions of this Agreement and
all such transactions.

         4.12 LAWS AND REGULATIONS. Notwithstanding any provision of this
Agreement to the contrary, no Party to this Agreement shall be required to take
any act, or fail to take any act, under this Agreement if the effect thereof
would be to cause such Party to be in violation of any applicable law, statute,
rule or regulation.

         4.13 NEGOTIATION OF RIGHTS OF LIMITED PARTNERS, ASSIGNEES, AND THIRD
PARTIES. The provisions of this Agreement are enforceable solely by the Parties
to this Agreement, and no limited partner, member, assignee or other Person of
the Partnership or General Partner shall have the right, separate and apart from
the Partnership or the General Partner, to enforce any provision of this
Agreement or to compel any Party to this Agreement to comply with the terms of
this Agreement.

                                       11
<PAGE>

               [REMAINDER OF THIS PAGE INTENTIONALLY LEFT BLANK.]

                                       12
<PAGE>

         IN WITNESS WHEREOF, the Parties hereto have executed this Omnibus
Agreement on, and effective as of, the date first written above.

                                    RIO VISTA ENERGY PARTNERS, L.P.

                                    By: RIO VISTA GP LLC,
                                        On behalf of itself and on behalf of
                                        Partnership as its General Partner

                                        By:________________________________
                                        Name:  Richard Shore, Jr.
                                        Title: President

                                    RIO VISTA OPERATING PARTNERSHIP L.P.

                                    By: RIO VISTA OPERATING GP LLC

                                        By: RIO VISTA ENERGY PARTNERS
                                            L.P., its sole member

                                            By: RIO VISTA GP LLC

                                                By:____________________________
                                                Name:__________________________
                                                Title:_________________________

                                    PENN OCTANE CORPORATION

                                    By:____________________________________
                                    Name:  Jerome B. Richter
                                    Title: President

                                       13
<PAGE>

                                  SCHEDULE 2.2

              PENDING LEGAL ACTIONS AGAINST PENN OCTANE CORPORATION

                                       14
<PAGE>

                                   SCHEDULE 4

                                    INSURANCE

                                       15

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