FOURTH
AMENDMENT TO

    SECURITIES PURCHASE AND SALE
AGREEMENT

    


    This
FOURTH AMENDMENT TO SECURITIES PURCHASE AND SALE AGREEMENT (this “Fourth
Amendment”) is entered into and effective as of this 17th day of
November, 2010 (the “Effective
Date”) by and among Central Energy, LP (“Buyer”),
Rio Vista Energy Partners, L.P. (the “Company”)
and Penn Octane Corporation (“Seller”).  Buyer,
the Company and Seller each a “Party” and
collectively the “Parties”.

     

    WHEREAS,
the Central Energy, LLC, the Company and Seller entered into that certain
Securities Purchase and Sale Agreement dated May 25, 2010 (the “Original
Agreement”), which Original SPA was subsequently amended by (a) an
Amendment to Securities Purchase and Sale Agreement dated July 1, 2010, (b) a
Second Amendment to Securities Purchase and Sale Agreement dated July 8, 2010,
(c) a Third Amendment to Securities Purchase and Sale Agreement dated July 21,
2010 and (d) letter agreements dated October 29, 2010 and November 5, 2010
extending the Outside Date (the Original Agreement, as so amended, the “Agreement”).

     

    WHEREAS,
pursuant to the provisions of Section 10(c) of the Agreement, Central Energy,
LLC has assigned all it its rights and obligations under the Agreement to Buyer
and Buyer has agreed to assume and be bound by the terms and provisions of the
Agreement as the assignee of Central Energy, LLC.

     

    WHEREAS,
the Parties are entering into this Fourth Amendment to further amend the
Agreement set out their agreement that a portion of the Purchase Price payable
under the Agreement for the Newly Issued Common Units will be in the form of a
promissory note payable by Buyer to Company in the principal amount of
$1,000,000 (the “Buyer’s
Note”) and to set out certain additional amendments to the
Agreement.

     

    WHEREAS,
capitalized terms not otherwise defined herein shall have the meanings ascribed
thereto in the Agreement.

     

    NOW
THEREFORE, for good and valuable consideration, the receipt and sufficiency of
which is hereby acknowledged, the Parties agree as follows:

     

    1.           Purchase Price. The
Parties hereby modify and amend existing Section 1(c) of the Agreement to read
as follows:

     

    “Purchase
Price.   The purchase price for the Newly Issued Common
Units shall be Three Million Eight Hundred Sixty Four Thousand Five Hundred
Forty One Dollars and No/100 ($3,864,541) (the “Common Unit
Purchase Price”).  Two Million Eight Hundred Sixty Four
Thousand Five Hundred Forty One Dollars and No/100 ($2,864,541) of the Common
Unit Purchase Price shall be payable by Buyer to Company in immediately
available funds on the Closing Date.  The remaining One Million
Dollars ($1,000,000) of the Common Unit Purchase Price shall be evidenced by a
promissory note (the “Buyer’s
Note”) in the form attached hereto as Exhibit “A” to be
delivered by Buyer to Company on the Closing Date.  The Common Unit
Purchase Price to be paid by Buyer to the Company and any additional amounts
contributed to the Company at Closing shall be held and utilized by the Company,
to the extent necessary, to satisfy Buyer’s conditions to closing set out in
Section 5(a)(ii) through (xii) hereof. The purchase price for the GP Interests
shall be One Hundred Forty Seven Thousand Nine Hundred and Fifty Nine Dollars
and No/100 ($147,959) (the “GP Interest
Purchase Price”) which amount shall be payable by Buyer to Seller in
immediately available funds on the Closing Date, with the GP Interest Purchase
Price then being immediately contributed by Seller to the GP and then by the GP
to the Company simultaneously with the Closing (the Common Unit Purchase Price
and the GP Interest Purchase Price, collectively, the “Purchase
Price”).”  Buyer’s obligations to timely pay the amounts due
and payable to Company under the terms of Buyer’s Note will be secured under the
terms an escrow agreement, in the form attached hereto as Exhibit “B” (the
“Escrow
Agreement”) to be executed by Buyer and Company on the Closing
Date.

     

    
      
         


      

      
         


        
          

        

      

      
         


      

    

     

    2.           Intercompany
Note.  The Parties hereby modify and amend existing Section
1(e) of the Agreement to read as follows:

     

    “Intercompany
Note.  At the Closing, the Company agrees to the satisfy out of
the Purchase Price that certain Promissory Note between the Seller and the
Company (the “Intercompany
Note”) for a minimum amount of $1,200,000, subject to adjustment as
follows (the “Intercompany Note
Settlement Amount”).  Schedule 5(a)(ix) will be updated as of the
Closing Date, by mutual agreement of the parties.  If as of the Closing
Date, such updated Schedule 5(a)(ix) reflects a Settled Surplus (as such term is
defined in Section 5(a)(ix)), then the Intercompany Note Settlement Amount shall
be increased by the amount of such Settled Surplus, up to a maximum of $200,000
(resulting in a maximum Intercompany Note Settlement Amount of
$1,400,000).” 

     

    3.           The
Closing.  The Parties hereby modify and amend existing Section
8(a) of the Agreement to read as follows:

     

    “The
Closing.  The Closing shall take place at the earliest possible
date (the “Closing
Date”) under this Agreement, but in any event not later than November 12,
2010 (as the same may be extended, the “Outside
Date”) at the offices of counsel for Buyer, SNR Denton US LLP, 2000
McKinney Ave., Suite 1900, Dallas, Texas 75201.  The date on which the
Closing actually occurs shall be the Closing Date.”

     

    4.           Documents at
Closing.  The Parties hereby modify and amend the existing
Section 8(b) of the Agreement as follows:

     

    A.          Section
8(b)(i)(4) is revised to read in its entirety as follows:

     

    
      	
               
      

            	
              “certificates
      representing the Newly Issued Common Units in the name of Buyer, with
      3,156,612 of such Newly Issued Common Units to be held by Company in
      escrow pursuant to the terms of the Escrow
  Agreement;

            


    

     

    
      	
               
      

            	
              B.

            	
              A
      new Section 8(b)(i)(5) is added which will read as follows with the
      remaining provisions of Section 8(b)(i) to be renumbered
      accordingly:

            


    

     

    
      	
               
      

            	
              “a
      duly executed Escrow Agreement;”

            


    

     

    
      
         


      

      
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              C.

            	
              A
      new Section 8(b)(iii)(3) is added which will read as follows with the
      remaining provisions of Section 8(b)(iii) to be renumbered
      accordingly:

            


    

     

    
      	
               
      

            	
              “a
      duly executed Escrow Agreement;”

            


    

     

    5.           Post
Closing.   The Parties hereby amend Article 9 to the
Agreement by adding a new subparagraph (b) which will read as
follows:

     

    b)           Piggy Back
Rights.  If the Company shall determine to prepare and file
with the Securities and Exchange Commission (the “SEC”) a
registration statement relating to an offering for its own account or the
account of others under the Securities Act of any of its equity securities, then
the Company shall send to Seller (so long as Seller is holding Common Units that
have not been covered by a registration statement that has been declared or
ordered effective), written notice of such determination and if, within 15
business days after receipt of such notice Seller shall so request in writing,
the Company shall include in such registration statement the Common Units
requested by Seller to be so included.  If Seller decides not to include
all of its Common Units in any registration statement thereafter filed by the
Company, Seller shall nevertheless continue to have the right to include any
Common Units in any subsequent registration statement or registration statements
as may be filed by the Company with respect to offerings of its securities, all
upon the terms and conditions set forth herein, to the extent all Common Units
held by Seller have not been covered by a registration statement that has been
declared or ordered effective by the time of such subsequent registration. 
If the registration statement under which the Company gives notice under this
Section is for an underwritten offering, the right of Seller to be included
in a registration pursuant to this Section shall be conditioned upon
Seller’s participation in such underwriting and the inclusion of Seller’s Common
Units in the underwriting to the extent provided herein.  Seller shall
enter into an underwriting agreement in a form substantially similar to the one
entered into by the Company with the underwriter or underwriters selected for
such underwriting by the Company.  Notwithstanding any other provision of
the Agreement, if the underwriter determines in good faith that marketing
factors require a limitation of the number of shares to be underwritten, the
number of shares that may be included in the underwriting shall be allocated,
first, to the Company; second, to any selling shareholders that shall have
exercised a demand registration right; third, on a pro rata basis, to Seller and
any other unitholders of the Company exercising incidental registration rights
based on the total number of Common Units sought to be registered in such
registration by  Seller and such other unitholders of the Company. 
 If Seller disapproves of the terms of any such underwriting, Seller may
elect to withdraw therefrom by written notice to the Company and the
underwriter, delivered at least ten (10) business days prior to the effective
date of the registration statement. The foregoing rights shall apply
equally to transferees of the Seller who are Affiliates (as defined in the
Partnership Agreement) thereof.

     

    
      
         


      

      
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    6.           Conduct of the Business of
the GP.  From the Closing Date until such time as the Senior
Obligation under Buyer’s Note (as defined therein) has been paid in full, the
Buyer shall cause the GP and the Company to conduct their business in the
ordinary course and shall not permit the GP or the Company to do any of the
following without first obtaining the written consent of the Insider
Group:

     

    a)           incur
any indebtedness for borrowed money;

     

    b)           declare
or pay any dividend or declare or make any distribution of any kind to any
holder of Common Units, or make any direct or indirect redemption, retirement,
purchase or other acquisition of any interests in the Company or any of the
Company’s Subsidiaries;

     

    c)           issue
any equity securities or rights to acquire such equity securities;
or

     

    d)           amend
this Agreement or the Buyer’s Note.

     

    7.           Acceptance of Terms of the
Partnership Agreement.  Buyer agrees that upon its receipt of
the Newly Issued Common Units on the Closing Date, it shall be deemed to have
(i) requested admission as, and agreed to become, a Limited Partner of the
Company and to have agreed to comply with and be bound by and to have executed
the First Amended and Restated Agreement of Limited Partnership of the Company
(as amended, the “Partnership
Agreement”)  (ii) represented and warranted that Buyer has all
right, power and authority to enter into the Partnership Agreement, (iii)
granted the powers of attorney provided for in the partnership Agreement and
(iv) made the waivers and given the consents and approvals contained in the
Partnership Agreement.

     

    8.           Acceptance of Terms of the
Company Agreement.  Buyer agrees that upon its receipt of the
GP Interests on the Closing Date, it shall be deemed to have (i) accepted and
agrees to be bound by the Amended and Restated Limited Liability Company
Agreement of the General Partner dated as of September 16, 2004, as amended by
the First Amendment thereto dated as of October 6, 2006.

     

    9.           Confirmation.  The
Parties hereby ratify, confirm, and adopt the Agreement, as amended
hereby.  Except as modified hereby, the Agreement shall remain in full
force and effect.

     

    10.         Headings.  The
headings in this Third Amendment are for reference purposes only and shall not
in any way affect the meaning or interpretation of this Third
Amendment.

     

    11.         Counterparts. This
Third Amendment may be executed in any number of counterparts, each of which
when so executed, shall constitute an original copy hereof, but all of which
together shall be considered but one and the same document.

     

    [Signatures on the
following page]

     

    
      
         


      

      
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    IN
WITNESS WHEREOF, the Parties hereto have executed and delivered this Fourth
Amendment as of the first date written above

     

    
      
        
          
            
              
                
                  
                    
                      
                        
                          
                            
                              
                                
                                  
                                    
                                      
                                        	 
      	
                                                COMPANY:

                                              
	 
      	 
      
	 
      	
                                                Rio
      Vista Energy Partners, L.P.

                                              
	 
      	 
      
	 
      	
                                                By: 

                                              	
                                                Rio
      Vista, GP LLC

                                              
	 
      	 
      	
                                                its
      General Partner

                                              
	 
      	 
      	 
      
	 
      	
                                                By:

                                              	
                                                /s/
      Ian T. Bothwell

                                              
	 
      	 
      	
                                                Ian
      T. Bothwell,

                                              
	 
      	 
      	
                                                President
      and Chief Executive Officer

                                              
	 
      	 
      
	 
      	
                                                Seller:

                                              
	 
      	 
      	 
      
	 
      	
                                                Penn
      Octane Corporation

                                              
	 
      	 
      	 
      
	 
      	
                                                By:

                                              	
                                                /s/
      Ian T. Bothwell

                                              
	 
      	
                                                Name:
      Ian T. Bothwell

                                              
	 
      	
                                                Title  Acting
      Chief Executive Officer and
President

                                              


                                      

                                    

                                  

                                

                              

                            

                          

                        

                      

                    

                  

                

              

            

          

        

      

    

     

    
      
        
          
            
              
                
                  
                    
                      	 	      
                              BUYER:

                            
	 
      	 
      
	 
      	
                              Central
      Energy, LP

                            
	 
      	 
      	 
      
	 
      	
                              By: 

                            	
                              /s/
      Carter R. Montgomery

                            
	 
      	Name: Carter
      R. Montgomery
	 
      	Title:   Managing
      Member
	 
      	 
      	 
      
	 
      	
                              By:

                            	
                              /s/
      Imad Anbouba

                            
	 
      	Name: Imad
      Anbouba
	 
      	Title:   Managing
      Member



                      
                        
                           


                        

                        
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