Document:

REPLACEMENT PROMISSORY NOTE

PROMISSORY  NOTE  (the  "Note")  of  the  Borrower  named below delivered to RZB
                         ----
Finance  LLC  ("RZB")  dated  September  15,  2004.
                ---

1.   SPECIAL  TERMS
     --------------

     The following terms and provisions shall apply to this Note; definitions of
     terms  in  this  or  other  sections of this Note expressed in the singular
     shall  include  the  plural  and  vice  versa.
                                       ----  -----

     Borrower:  Penn  Octane  Corporation
     --------

     a  Delaware  Corporation
     (jurisdiction  of  incorporation)

     Principal  Amount  of  this  Note:
     ---------------------------------

     Fifteen  Million  Dollars

     ($15,000,000)

     Margin:  2.5%  p.a.
     ------

     Loan Documents:  Amended and Restated Line Letter dated September 15, 2004,
     --------------
     between the Borrower and RZB, General Security Agreement dated February 13,
     2002,  between  the  Borrower  and RZB, Continuing Agreement for Letters of
     Credit  dated  October 14, 1997, between the Borrower and RZB, Guaranty and
     Agreement  dated  October 14, 1997 between Jerome Richter and RZB, Guaranty
     and  Agreement  dated  September 15, 2004 between Rio Vista Energy Partners
     L.P.  and  RZB  and Guaranty and Agreement dated September 15, 2004 between
     Rio Vista Operating Partnership L.P. and RZB, and all other agreements from
     time  to  time  executed  by  the Borrower or any of the guarantors for the
     benefit of RZB, in each case as amended, modified or supplemented from time
     to  time.

     Minimum  Repayment  Amount:  N/A
     --------------------------

2.   PRINCIPAL  AND  INTEREST
     ------------------------

     FOR  VALUE  RECEIVED,  the Borrower promises to pay to the order of RZB, ON
     DEMAND,  the  Principal  Amount  of this Note specified in Section 1 or, if
     less, the then-outstanding principal amount of all loans (each a "Loan" and
                                                                       ----
     collectively, the "Loans") made to the Borrower by RZB pursuant to the Loan
                        -----
     Documents.  In no event shall the maturity date of any Loan be more than 30
     days  after  the  date  such  Loan  is  made.

     The  Borrower  promises also to pay interest on the unpaid principal amount
     of each Loan (after as well as before judgment) from the date thereof until
     maturity  (whether  on  demand, by acceleration or otherwise) at a rate per
     annum equal to the Margin specified in Section 1 plus the Base Lending Rate
     from  time  to  time  in  effect,  such  interest to be payable on the last
     Business  Day  of  each  calendar  month  and  at  such  maturity.

     Notwithstanding  the  preceding  sentence,  the  Borrower  shall  also  pay
     interest  at  a  rate  per  annum equal to 2% plus the Margin plus the Base
     Lending Rate from time to time in effect, on any principal of the Loan and,
     to  the extent permitted by law, on any interest or other amount payable by
     the Borrower hereunder which shall not be paid in full when due (whether on
     demand, by acceleration or otherwise) from such due date until paid in full
     (after  as well as before judgment), such interest to be payable on demand.

     All  interest shall be computed on the basis of the number of days actually
     elapsed  in  a  360-day  year.

     Definitions
     -----------

     The term "Business Day" means any day other than a Saturday, Sunday, or any
               ------------
     day  which  shall  be  in  New  York City a legal holiday or a day on which
     banking  institutions  are  authorized  by  law  to  close.

     The term "Base Lending Rate" means, for any day, the higher of (i) the rate
               -----------------
     announced by The Chase Manhattan Bank (the "Bank") from time to time at its
     principal  office  in  New  York,  New  York as its prime rate for domestic
     (United States) commercial loans in effect on such day and (ii) the Federal
     Funds  Rate in effect on such day plus 1/2%. (Such Base Lending Rate is not
     necessarily  intended to be the lowest rate of interest charged by the Bank
     in  connection  with extensions of credit.) Each change in the Base Lending
     Rate  shall  result in a corresponding change in the interest rate and such
     change  shall be effective on the effective date of such change in the Base
     Lending  Rate.

     The  term  "Federal  Funds  Rate" means, for any day, the overnight federal
                 --------------------
     funds  rate in New York City, as published for such day (or, if such day is
     not  a  Business  Day,  for the next preceding Business Day) in the Federal
     Reserve  Statistical Release H.15 (519) or any successor publication, or if
     such  rate  is  not  so  published for any day which is a Business Day, the
     average  of  the  quotations  for  such  day  on  overnight  federal  funds
     transactions in New York City received by the Bank from three federal funds
     brokers  of  recognized  standing  selected  by  the  Bank.

                                      -1-
<PAGE>
3.   ALL  PAYMENTS
     -------------

     Each  payment  by the Borrower pursuant to this Note shall be made prior to
     1:00 P.M. (New York time) on the date due and shall be made without set-off
     or  counterclaim  to  RZB at such account as RZB shall designate, or in the
     absence  of  such  designation,  to RZB at its office, presently located at
     1133  Avenue  of  the Americas, New York, NY 10036, or as RZB may otherwise
     direct  and  in  such  amounts  as  may be necessary in order that all such
     payments  (after  withholding  for  or  on account of any present or future
     taxes,  levies,  imposts,  duties  or  other  similar charges of whatsoever
     nature  imposed  by  any  government or any political subdivision or taxing
     authority  thereof,  other than any tax on or measured by the net income of
     RZB  pursuant  to  the  income  tax  laws  of  the jurisdiction where RZB's
     principal  or lending office is located) shall not be less than the amounts
     otherwise  specified to be paid under this Note. Each such payment shall be
     made  in lawful currency of the United States of America and in immediately
     available  funds.  If the stated due date of any payment required hereunder
     is  other  than  a  Business  Day,  such  payment shall be made on the next
     succeeding  Business  Day  and interest at the applicable rate shall accrue
     thereon  during  such  extension.

     The  Borrower  will  have  the  right to repay all or any portion of a Loan
     prior to demand only if RZB has been notified prior to 10:00 a.m. (New York
     time)  on  the  day  of any repayment, provided that each partial repayment
     shall  not  be  less  than  the  Minimum  Repayment  Amount. All repayments
     pursuant  to  this  paragraph  shall  be  accompanied by the payment of all
     accrued  interest  on  the  principal  amount  so  paid.

4.   REPRESENTATIONS  AND  WARRANTIES
     --------------------------------

     The Borrower represents and warrants that all acts, filings, conditions and
     things  required  to be done and performed and to have happened (including,
     without  limitation,  the  obtaining  of  necessary governmental approvals)
     precedent  to  the  issuance  of this Note to constitute this Note the duly
     authorized,  legal,  valid  and  binding  obligation  of  the  Borrower,
     enforceable  in  accordance  with  its terms, have been done, performed and
     have  happened  in  due  and  strict  compliance  with all applicable laws.

5.   DEFAULT
     -------

     Without  limiting the right of RZB to demand payment of the Loans evidenced
     hereby  at  any time in its sole discretion, if any of the following events
     shall  occur:  default in payment of any amount due hereunder to the holder
     hereof,  whether  on  demand or otherwise; suspension or liquidation by the
     Borrower  of  its usual business or suspension or expulsion of the Borrower
     from  any  exchange;  calling  of a meeting of creditors; assignment by the
     Borrower  for  the  benefit  of creditors; dissolution, bulk sale or notice
     thereof  effected or given by the Borrower; creation of a security interest
     in  any  assets  of  the  Borrower  which  are or shall be subject to liens
     granted  to the holder hereof by the Borrower without consent of the holder
     hereof;  insolvency  of any kind, attachment, distraint, garnishment, levy,
     execution,  judgment,  application  for  or  appointment  of  a receiver or
     custodian,  filing  of  a  voluntary  or  involuntary  petition  under  any
     provision  of  the  U.S.  Bankruptcy  Code or amendments thereto, of, by or
      against  the Borrower or any property or rights of the Borrower; filing of
      a petition or institution of any proceeding by or against the Borrower for
      any relief under any bankruptcy or insolvency laws or any laws relating to
      the  relief  of  debtors,  readjustment  of indebtedness, reorganizations,
      compositions or extensions; any governmental authority or any court at the
      instance  of  any  governmental  authority  shall  take  possession of any
      substantial  part  of the property of the Borrower or shall assume control
      over  the  affairs  or  operations  of  the  Borrower;  any  statement,
      representation or warranty made by the Borrower in any document, agreement
      or  financial  statement  delivered  to RZB shall prove to be false in any
      material  respect  when  made;  failure of the Borrower or any other party
      thereto  to  comply with any term of any of the Loan Documents; failure of
      the  Borrower, on request, to furnish to RZB any financial information, or
      to  permit  inspection  by  RZB of any books or records; any change in, or
      discovery  with regard to, the condition or affairs of the Borrower which,
      in  RZB's  opinion,  increases  its  credit  risk; or if RZB for any other
      reason  deems  itself  insecure;  then, the indebtedness evidenced by this
      Note,  and  all  accrued  interest  thereon shall become absolute, due and
      payable  without demand or notice to the Borrower. Upon default in the due
      payment of this Note, or whenever the same or any installment of principal
      or  interest  hereof  shall  become  due  in  accordance  with  any of the
      provisions hereof (whether on demand or otherwise), RZB may, but shall not
      be  required  to,  exercise any or all of its rights and remedies, whether
      existing  by  contract,  law  or otherwise, with respect to any collateral
      security  delivered  in  respect  of  the  indebtedness  evidenced hereby.

6.   MISCELLANEOUS
     -------------

     This  Note  is  delivered pursuant to, and entitled to the benefits of, the
     Loan  Documents.

     The  Loans  and principal repayments thereof may be recorded on the records
     of  RZB and, prior to any transfer of, or any action to collect, this Note,
     the  outstanding  principal  amount  of each Loan shall be endorsed on this
     Note,  together  with the date of such endorsement. Any such recordation or
     endorsement  shall  constitute  prima facie evidence of the accuracy of the
                                     -----  -----
     information so recorded or endorsed (provided, however, that the failure of
     RZB  to record any of the foregoing shall not limit or otherwise affect the
     obligation  of  the  Borrower  to  repay  all the Loans (including interest
     thereon) and its other obligations hereunder and under the Loan Documents).
     The  Bank  may charge any account of the Borrower with the Bank for amounts
     payable  under  this  Note.

     Each payment of principal of, or interest on, the Loans shall constitute an
     acknowledgment of the indebtedness of the Borrower under the Loan Documents
     and  this  Note.  The  Borrower:

     a.   waives  presentment,  demand,  protest and other notice of any kind in
          connection  with  this  Note,  and

     b.   agrees  to pay to the holder hereof, on demand, all costs and expenses
          (including  reasonable  legal  fees)  incurred  in connection with the
          enforcement  and  collection  of  this  Note.

     THIS  NOTE SHALL BE CONSTRUED IN ACCORDANCE WITH AND GOVERNED BY THE LAW OF
     THE  STATE  OF NEW YORK (WITHOUT REGARD TO PRINCIPLES OF CONFLICTS OF LAW),
     BUT  THIS  SHALL NOT LIMIT THE RATE OF INTEREST WHICH MAY BE CHARGED BY RZB
     UNDER  OTHER  APPLICABLE  LAW.

     The  Borrower hereby agrees that ANY LEGAL ACTION OR PROCEEDING AGAINST THE
     BORROWER  WITH

                                      -2-
<PAGE>
     RESPECT  TO THIS NOTE MAY BE BROUGHT IN THE COURTS OF THE STATE OF NEW YORK
     IN THE CITY OF NEW YORK OR OF THE UNITED STATES OF AMERICA FOR THE SOUTHERN
     DISTRICT  OF  NEW  YORK  as  RZB  may elect, and, by execution and delivery
     hereof,  the Borrower accepts and consents to, for itself and in respect to
     its  property,  generally  and  unconditionally,  the  jurisdiction  of the
     aforesaid  courts  and  agrees  that  such jurisdiction shall be exclusive,
     unless  waived  by RZB in writing, with respect to any action or proceeding
     brought  by  it  against  RZB  and any questions relating to usury. Nothing
     herein  shall  limit  the  right  of  RZB  to bring proceedings against the
     Borrower in the courts of any other jurisdiction. Service of process out of
     any  such  courts  may  be  made by mailing copies thereof by registered or
     certified mail, postage prepaid, to the Borrower at its address for notices
     as  specified  herein and will become effective 30 days after such mailing.
     The  Borrower  agrees  that  Sections  5-1401  and  5-1402  of  the General
     Obligations  Law  of the State of New York shall apply to this Note and, to
     the maximum extent permitted by law, waives any right to stay or to dismiss
     any  action  or proceeding brought before said courts on the basis of forum
                                                                           -----
     non conveniens.
     --- ----------

     AFTER  REVIEWING  THIS  PROVISION SPECIFICALLY WITH ITS RESPECTIVE COUNSEL,
     EACH  OF  THE  BORROWER  AND  RZB  HEREBY  KNOWINGLY,  VOLUNTARILY  AND
     INTENTIONALLY  WAIVES  ANY AND ALL RIGHTS IT MAY HAVE TO A TRIAL BY JURY IN
     RESPECT  OF  ANY  LITIGATION  BASED  ON,  OR  ARISING  OUT OF, UNDER, OR IN
     CONNECTION  WITH,  THIS  NOTE  OR ANY COURSE OF CONDUCT, COURSE OF DEALING,
     STATEMENTS  (WHETHER VERBAL OR WRITTEN), OR ACTIONS OF THE BORROWER OR RZB.
     THIS  PROVISION  IS  A  MATERIAL INDUCEMENT FOR RZB MAKING THE LOANS TO THE
     BORROWER.

     Nothing  contained in this Note shall be deemed to establish or require the
     payment  of  a  rate of interest in excess of the maximum rate permitted by
     applicable  law (the "Maximum Rate"). If the amount of interest payable for
                           ------------
     any  interest payment period ending on any interest payment date calculated
     in  accordance  with  the  provisions  of  this  Note  (said  amount,  the
     "Calculated Interest") exceeds the amount of interest that would be payable
      -------------------
     for  such  interest  payment  period had interest for such interest payment
     period  been  calculated  at  the Maximum Rate, there shall be paid on such
     interest  payment date an amount of interest calculated on the basis of the
     Maximum  Rate  for  such  interest  payment  period.  If  on any subsequent
     interest payment date, (i) the Calculated Interest for the interest payment
     period  ending  on  such  subsequent  interest  payment  date (the "Current
                                                                         -------
     Interest Period") is less than the amount of interest that would be payable
     ---------------
     for  such  Current  Interest  Period had interest for such Current Interest
     Period  been  calculated  on  the  basis  of  the Maximum Rate and (ii) any
     portion  of  the  excess  (if  any)  of  Calculated  Interest for any prior
     interest  payment  period  over interest calculated at the Maximum Rate for
     such  prior  interest  payment  period  (the "Outstanding Interest Amount")
                                                   ---------------------------
     remains  unpaid,  then on such subsequent interest payment date there shall
     be  paid, as provided herein, additional interest for such Current Interest
     Period  in  an  amount  equal  to  the lesser of (i) the theretofore unpaid
     Outstanding Interest Amounts for all prior interest payment periods or (ii)
     an amount that, when added to the amount of Calculated Interest payable for
     such  Current  Interest Period, results in the payment of interest for such
     Current  Interest  Period  at  the  Maximum  Rate.

     This  Note replaces but does not constitute payment or satisfaction of or a
     novation  of  the  Promissory  Note  dated  May  19,  2000  executed by the
     undersigned  to  the  order  of  RZB.

          IN  WITNESS  WHEREOF,  the undersigned has caused this Note to be duly
     executed  and  delivered  by  its  duly  authorized  officer(s).

     PENN  OCTANE  CORPORATION

     By /s/ Jerome B. Richter
        ------------------------------
      Name:  Jerome B. Richter
      Title: Chief Executive Officer

     Address of Borrower for Notices:

     77-530 Enfield Lane
     Building D
     Palm Desert, CA  92211

                                      -3-
<PAGE>Consent Letter
                                 --------------

                                                       September 15, 2004

Penn Octane Corporation
77-530 Enfield Lane
Building D
Palm Desert, CA  92211
Attention:  Mr. Jerome Richter

Gentlemen:

1.   Reference  is  made  to the line letter dated October 14, 1997, as amended,
between  you  and  us,  providing  for  extensions  of  credit  to  Penn  Octane
Corporation  ("Penn  Octane")  in  the  form of loans and letters of credit (the
"Line Letter").  Capitalized terms used herein and not defined herein shall have
the  meanings  ascribed  thereto  in  the  Line  Letter.

2.   You  have  advised  us  that  Penn  Octane  is  proposing  a  corporate
reorganization  (the  "Reorganization")  as  follows.  Penn Octane will transfer
substantially  all  of  its  pipeline and terminal assets to Rio Vista Operating
Partnership  L.P., a Delaware limited partnership (the "Operating Partnership"),
which  is  a  wholly  owned  subsidiary  of  Rio  Vista Energy Partners L.P.,  a
Delaware  limited  partnership  ("Rio Vista"), which is currently a wholly owned
subsidiary  of  Penn  Octane.  Rio  Vista  will  be  spun  off  to Penn Octane's
stockholders  by  means of a pro rata distribution to them of 100% of the common
units  of  Rio  Vista.  As  a  result  of  such  spin-off,  Rio Vista will be an
independent  public  company, and Penn Octane will not directly own any units of
Rio  Vista but will have an at least 50% ownership interest in, and (pursuant to
a  voting agreement with other members) voting control over, the general partner
of  Rio  Vista,  Rio  Vista  GP  LLC,  a Delaware limited liability company (the
"RVGP").  Rio  Vista  will  own  all of the limited partnership interests in the
Operating  Partnership and all of the limited liability company interests in the
general  partner  of  the Operating Partnership, Rio Vista Operating GP LLC (the
"OPGP").  Penn  Octane  and the Operating Partnership will enter into a purchase
contract pursuant to which the Operating Partnership will purchase LPG from Penn
Octane,  and the Operating Partnership will sell the LPG to customers acceptable
to  RZB.

3.   RZB confirms that it approves and consents to the Reorganization subject to
the  following  conditions:

     (a)  Nothing  contained  herein  shall modify or waive any provision of the
Line  Letter  providing  for  the  uncommitted and demand nature of RZB's credit
facility (including, without limitation, Sections 1 and 4 thereof).

     (b)  You  shall  deliver  to  RZB  copies  of  all  documents,  agreements,
instruments  and  SEC  filings  relating to the Reorganization, which must be in
form and substance satisfactory to RZB and certified as true and complete by the
chief executive officer or chief financial officer of Penn Octane.

     (c)  RZB  shall  receive,  in form and substance satisfactory to it, all of
the  agreements,  instruments and documents listed in the attached closing list.

                                      -1-
<PAGE>
     (d)  RZB shall receive, in form and substance satisfactory to it, pro forma
balance  sheets of each of the parties referred to above (including Penn Octane,
Rio  Vista, the Operating Partnership, RVGP and OPGP) after giving effect to the
Reorganization,  certified  as true and complete by the chief executive or chief
financial  officer  of  Penn  Octane.

Notwithstanding any other Loan Documents, RZB also consents to and agrees to
subordinate its liens and security interests in all of Penn Octane's and/or Rio
Vista's assets, personal property, fixtures, intangibles and property
constituting Collateral (as defined in the Loan Documents), except the following
assets of Penn Octane, Rio Vista and/or the Operating Partnership as to which
RZB shall have at all times a first priority perfected lien (i) cash held in
Penn Octane's, Rio Vista's or the Operating Partnership's accounts at RZB JP
Morgan Chase Bank, Service 1st Bank or any other bank which maintains accounts
subject to a control agreement in favor of RZB, (ii) inventory of every type and
description, whether raw, in process or finished and all documents, documents of
title and receipts covering any inventory and all products and proceeds thereof;
(iii) accounts, accounts receivable, contract rights, general intangibles,
payment intangibles, tax refund claims, instruments, promissory notes, chattel
paper, supporting obligations, letters of credit and letter-of-credit rights and
other rights to payment of money and all products and proceeds thereof; (iv) the
lease and other collateral described in Leasehold Deed of Trust, Security
Agreement, Financing Statement and Assignment of Rents dated October 17, 1997,
filed for record on January 14, 1998, under Cameron County Clerk's File No. 1243
and filed for record on January 20, 1998, under Kleberg County Clerk's File No.
222368, Kenedy County Clerk's File No. 5694, Willacy County Clerk's File No.
274128 and Jim Wells County Clerk's File No. 311304, as amended, modified and
supplemented from time to time , including, without limitation,  Lease Agreement
dated September 1, 1993, between the Seadrift Pipeline Corporation, as Lessor,
and Borrower, as Lessee, as amended, modified and supplemented from time to
time, including, without limitation, by Agreements dated October 10, 1993 and
May 21, 1997; (v) Penn Octane's LPG supply agreements and all other agreements
providing for or relating to purchase of inventory of every type by Penn Octane,
Rio Vista and/or the Operating Partnership, all claims thereunder and all rights
and remedies relating thereto and (vi) all agreements with P.M.I. Trading
Limited or any affiliate or subsidiary thereof, as to all of the foregoing items
in clauses (i) through and including (vi), whether now owned or existing or
hereafter acquired or arising and wherever located (all such property, except
the property described in clauses (i) through and including (vi), the
"Subordinated Collateral").

Accordingly,  RZB  consents  that  the Subordinated Collateral can be pledged by
Penn  Octane  to  its existing creditors (which shall be deemed to include those
creditors  which  may  substitute  as  note  holders in connection with existing
indebtedness, and the holders of any indebtedness incurred to refinance existing
indebtedness)  and  RZB  agrees  that  it  shall not take any action which would
prevent  such  creditors (the "Senior Creditors") from foreclosing and enforcing
liens  superior  to RZB in such Subordinated Collateral in the event Penn Octane
is  in  default  under  the  related indebtedness, provided, however, that RZB's
                                                   --------  -------
agreements  in  this  paragraph  4  shall  not be effective unless and until the
Senior  Creditors  shall  have  duly  executed and delivered a valid and binding
agreement  pursuant  to  which  they  agree  that:

     (w)  They shall not take any action which would prevent RZB from
foreclosing and enforcing its liens on all Collateral, other than Subordinated
Collateral.

     (x)  They shall agree not to challenge or dispute (a) the validity,
perfection or priority of RZB's security interest in any Collateral (other than
Subordinated Collateral), or (b) any relief

                                      -2-
<PAGE>
requested by RZB to protect or realize on its Collateral (other than
Subordinated Collateral) in any bankruptcy case with respect to the Company
including, without limitation, any cash collateral order or debtor-in-possession
financing.

     (y)  They shall agree that this paragraph 4 is solely for the benefit of
RZB and the Senior Creditors and their successors and assigns and no other
person shall have any right or benefit under or because of the existence of this
paragraph 4.

     (z)  They shall agree to permit use of any collateral subject to their
senior security interest (including all Subordinated Collateral) for storage,
processing, transportation or delivery of RZB's Collateral for a period of 60
days after notice from the Senior Creditors or their representative to RZB or
from RZB to Penn Octane of the beginning of such 60-day period, all without
charge, cost or expense to RZB.

4.   Pursuant  to  the final sentence of Section 7.3(b) of the First Amended and
Restated  Agreement  of  Limited  Partnership  of  Rio  Vista (the "Rio Vista LP
Agreement"),  Penn Octane, as holder of the Unit Majority (as defined in the Rio
Vista  LP  Agreement)  on  the date hereof, approves all action taken by RVGP on
behalf  of  Rio  Vista in connection with the authorization, execution, delivery
and/or  performance  of  the agreements, instruments and documents listed on the
attached  closing  list, including all action (if any) so taken on behalf of Rio
Vista  which  constitutes  action  permitted  to  be  taken  by a partner of the
Operating  Partnership  within the meaning of clause (ii) of such final sentence
of  Section  7.3(b)  of  the  Rio  Vista  LP  Agreement.

5.   (a)  This  Consent  shall  be a "Loan Document" as such term is used in the
Line  Letter  and  the  other  Loan  Documents.

     (b)  No  delay  on the part of RZB in exercising any of its options, powers
or  rights, or partial or single exercise thereof, irrespective of any course of
dealing,  shall  constitute a waiver thereof.  The options, powers and rights of
RZB  specified  herein  and in the other Loan Documents are in addition to those
otherwise created by law or under any other agreement between any Loan Party and
RZB.  No  amendment,  modification  or  waiver of any provision hereof or of any
Loan  Document  to which any Loan Party is a party, nor consent to any departure
by  any  Loan  Party  therefrom, shall be effective, unless the same shall be in
writing  and  signed by RZB.  Any such waiver or consent shall be effective only
in  the specific instance and for the purpose for which given.  No consent to or
demand  on  any Loan Party in any case shall, of itself, entitle it to any other
or  further  notice  or  demand  in  similar  or  other  circumstances.

     (c)  This  Consent and the other Loan Documents embody the entire agreement
and  understanding  between  RZB  and  the  Loan Parties and supersede all prior
agreements and understandings relating to the subject matter hereof and thereof.
THIS  WRITTEN  AGREEMENT  (AND  THE  OTHER  LOAN DOCUMENTS) REPRESENTS THE FINAL
AGREEMENT  AMONG  THE  PARTIES HERETO AND THE OTHER LOAN PARTIES WITH RESPECT TO
THE  MATTERS  COVERED HEREBY AND THEREBY AND MAY NOT BE CONTRADICTED BY EVIDENCE
OF PRIOR, CONTEMPORANEOUS OR SUBSEQUENT ORAL AGREEMENTS OF THE PARTIES.

                                      -3-
<PAGE>
     (d)  THIS  AGREEMENT  SHALL BE CONSTRUED IN ACCORDANCE WITH AND GOVERNED BY
THE  LAW  OF THE STATE OF NEW YORK (WITHOUT REGARD TO PRINCIPLES OF CONFLICTS OF
LAW).

                                         Very truly yours,

                                         RZB FINANCE LLC

                                         By: /s/ Pearl Geffers
                                            ---------------------------
                                            Name:  Pearl Geffers
                                            Title: First Vice President

                                         By: /s/Griselda Alvizo
                                            ---------------------------
                                            Name:  Griselda Alvizo
                                            Title: Vice President

Accepted and Agreed to on this 15th day of
                               ----
September, 2004
---------

PENN OCTANE CORPORATION

By: /s/ Jerome B. Richter
   ------------------------------
   Name:  Jerome B. Richter
   Title: Chief Executive Officer

The undersigned hereby acknowledges and consents
to the foregoing Consent Letter and hereby confirms
that the Guaranty and Agreement dated as of October
14, 1997 is hereby ratified and confirmed in all
respects.

/s/ Jerome B. Richter
---------------------------------
    Jerome Richter

                                      -4-
<PAGE>
                                 RZB FINANCE LLC
                                       AND
                             PENN OCTANE CORPORATION

                                  CLOSING LIST

1.   Amended and Restated Line Letter

2.   Promissory Note

3.   Certificate for

     i.    Penn Octane
     ii.   Rio Vista Energy Partners L.P. ("RVEP")
     iii.  Rio Vista Operating Partnership L.P. ("Operating Partnership")

     as to

     (a)  Certificate  of  incorporation (Penn Octane); certificate of formation
          (RVEP  and  Operating  Partnership)
     (b)  By-laws  (Penn  Octane);  partnership  agreement  (RVEP  and Operating
          Partnership)
     (c)  Resolutions
     (d)  Incumbency

4.   Opinions of counsel to Loan Parties

5.   Guarantees from

     (a)  Mr. Jerome Richter (re-affirmation of guarantee previously delivered)
     (b)  RVEP
     (c)  Operating Partnership

6.   Security Agreements from

          (a)  Penn Octane (previously delivered)
          (a)  RVEP
          (b)  Operating Partnership

7.   Security Agreement Questionnaires from

          (a)  Penn Octane
          (a)  RVEP
          (b)  Operating Partnership

                                      -5-
<PAGE>
8.   Lien searches for

          (a)  Penn Octane
          (b)  RVEP
          (c)  Operating Partnership

9.   UCC-1's against

          (a)  Penn Octane (previously filed)
          (b)  RVEP
          (c)  Operating Partnership

10.  Notice to account debtors sent by the Operating Partnership (including to
PMI) duly executed by account debtors and evidence of signature authority
satisfactory to RZB

11.  Evidence of insurance and loss payable endorsements

     (a)  Penn Octane
     (b)  RVEP
     (c)  Operating Partnership

12.  Certified copies of supply and sales contracts

     (a)  Penn Octane
     (b)  Operating Partnership

13.  Lockbox arrangements with respect to

     (a)  Penn Octane
     (b)  Operating Partnership

14.  Certified copies of SEC filings, agreements, documents, etc., relating to
operation, etc., and transfer by Borrower of its assets

     (a)  Penn Octane
     (b)  RVEP
     (c)  Operating Partnership

                                    *   *   *

                                      -6-
<PAGE>
Real Estate Documents
---------------------

15.  Certified copy of lease and all amendments

     (a)  Terminal
     (b)  Pipeline

16.  Recorded notices of lease

     (a)  Terminal
     (b)  Pipeline

17.  Modification Agreements for Deeds of Trust

     (a)  Terminal
     (b)  Pipeline

18.  Landlord consent and agreement

     (a)  Terminal
     (b)  Pipeline

19.  Mortgagee's insurance policy in the amount of $1,000,000 with revolving
loan rider

     (a)  Terminal
     (b)  Pipeline [NOTE - NOT AVAILABLE]

20.  Survey certified to the Lender

     (a)  Terminal
     (b)  Pipeline [NOTE - NOT NORMALLY AVAILABLE]

21.  Copies of plats and field notes for terminal, all satisfactory to RZB

22.  Permits, etc.

     (a)  Certificate of Occupancy for Terminal
     (b)  T-4 Railroad Commission permit for Pipeline

     certified as true and complete and as constituting all necessary permits by
     appropriate officer of the Borrower

23.  Re-recording of Deeds of Trust and recording of ratification by grantors
for

     (a)  Terminal
     (b)  Pipeline

                                      -7-
<PAGE>
     [IN FOUR YEARS] [RZB TO ADDRESS POST-CLOSING]

24.  Good standing, etc.

     (a)  Texas good standing certificate
     (b)  Texas certificate of qualification

     for

     (c)  Penn Octane
     (d)  RVEP
     (e)  Operating Partnership

25.     Certified director resolutions authorizing Modification Agreements to
Deeds of Trust for

     (a)  Penn Octane
     (b)  Operating Partnership

                                      -8-
<PAGE>

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