REPLACEMENT PROMISSORY NOTE


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


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3.   ALL  PAYMENTS
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     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


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     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


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