Exhibit 10.1
 FIRST AMENDMENT TO NOTE PURCHASE AGREEMENT
 Amendment 44 Company Administrative
Agent Holders
  Original Agreement
    DEFINITIONS AND REFERENCES
 Terms Defined in the Original Agreement
 Other Defined Terms
 Amendment
 Amendment Documents
 [First Amendment to  Note Purchase Agreement]




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Designated Defaults
       Note Purchase Agreement
 Released Claims
 Released Persons
 [First Amendment to  Note Purchase Agreement]
  2




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AMENDMENTS & WAIVERS
 Interest Rate
  Fixed Rate
 Hedging Contract
  Effective Rate Certificate
 Existing Litigation
 Recalculation Date
 [First Amendment to  Note Purchase Agreement]
  3




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Interest Rates
 Applicable Date Effective Rate Certificate
   Mandatory Prepayments
 Books, Financial Statements and Reports
   Disclosure Schedule
 Holders Schedule
 Approved Plan of Development
 Limited Waivers
 [First Amendment to  Note Purchase Agreement]
  4




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CONDITIONS OF EFFECTIVENESS
 Effective Date
 Amendment Documents
 Good Standing Certificates
 Up-Front Payment
 Closing Certificate
 Completion of Proceedings
 Other Documentation
 No Default
 Payment of Expenses
 [First Amendment to  Note Purchase Agreement]
  5




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REPRESENTATIONS AND WARRANTIES
 Representations and Warranties of Company
      [First Amendment to  Note Purchase Agreement]
  6




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Rio Vista Penny, LLC  Operating Account
    
    
    #6524272Rio Vista Penny, LLC  Savings Account
    
    
    #494512Rio Vista Penny, LLC  CD #1
    
    
    #27770Rio Vista Penny, LLC  CD #2
    
    
    #27888Rio Vista Penny, LLC  Custody Account
    
    
    #6524250Rio Vista Operating, LLC  Checking
    
    
    #6524239Rio Vista Operating, LLC  Payroll Account
    
    
    #6524195
   MISCELLANEOUS
 Ratification; Acknowledgments; No Waiver
 Ratification
 Acknowledgment of Designated Defaults
 [First Amendment to  Note Purchase Agreement]
  7




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No Waiver
 Release of Claims . To induce Holder Parties to enter into this
Agreement, each Restricted Person hereby (a) represents and warrants that as of the date of this
Agreement there are no claims or offsets against or defenses or counterclaims to its obligations
under the Note Documents, and waives any and all such claims, offsets, defenses, or counterclaims,
whether known or unknown, arising prior to the date of this Agreement, (b) releases and forever
discharges the Released Persons from any and all Released Claims, and (c) covenants not to assert
(and not to assist or enable any other Person to assert) any Released Claim against any Released
Person. The Restricted Persons acknowledge and agree that such release is a general release of any
and all Released Claims that constitutes a full and complete satisfaction for all or any alleged
injuries or damages arising out of or in connection with the Released Claims, all of which are
herein compromised and settled.
 Reviewed by Attorneys
 [First Amendment to  Note Purchase Agreement]
  8




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Survival of Agreements
 Note Documents
 Governing Law Except to the extent that the law of another
jurisdiction is expressly elected in a Note Document, this Amendment and the other Amendment
Documents shall be governed by and construed in accordance with the internal laws of the State of
New York, without regard to principles of conflicts of laws.
 Counterparts; Fax
 This written Agreement and the other Note Documents represent the final agreement between
the parties and may not be contradicted by evidence of prior, contemporaneous, or subsequent oral
agreements of the parties.
 There are no unwritten oral agreements between the parties.
 The remainder of this page has been intentionally left blank.
 [First Amendment to  Note Purchase Agreement]
  9




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COMPANY:
RIO VISTA PENNY LLCBy:Ian BothwellManager [Signature Page to First Amendment to  Note Purchase Agreement]




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ADMINISTRATIVE AGENT:TCW ASSET MANAGEMENT COMPANY,
Administrative AgentBy:Name:Title:By:Name:Title:HOLDERS:TCW ENERGY FUND X  NL, L.P.,
a California limited partnershipBy:
    
    TCW (ENERGY X) LLC, its General Partner:By:
    
    TCW Asset Management Company,
its Managing MemberBy:Name:Title:By:Name:Title:
 [Signature Page to First Amendment to  Note Purchase Agreement]




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TCW ENERGY FUND XB  NL, L.P.,
a California limited partnershipBy:
    
    TCW (ENERGY X) LLC, its General Partner:By:
    
    TCW Asset Management Company,
its Managing MemberBy:Name:Title:By:Name:Title:TCW ENERGY FUND XC  NL, L.P.,
a California limited partnershipBy:
    
    TCW (ENERGY X) LLC, its General Partner:By:
    
    TCW Asset Management Company,
its Managing MemberBy:Name:Title:By:Name:Title:
 [Signature Page to First Amendment to  Note Purchase Agreement]




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TCW ENERGY FUND XD  NL, L.P.,
a California limited partnershipBy:
    
    TCW (ENERGY X) LLC, its General Partner:By:
    
    TCW Asset Management Company,
its Managing MemberBy:Name:Title:By:Name:Title:TCW ASSET MANAGEMENT COMPANY, a California
corporation, as Investment Manager under the Amended 
and Restated Investment Management and Custody 
Agreement dated as of December 3, 2003 among Ensign
Peak Advisors, Inc., TCW Asset Management Company and
Trust Company of the West, a California trust
company, as Sub-CustodianBy:Name:Title:By:Name:Title:
 [Signature Page to First Amendment to  Note Purchase Agreement]




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TCW ASSET MANAGEMENT COMPANY, a California
corporation, as Investment Manager under the Amended
and Restated Investment Management and Custody
Agreement dated as of December 11, 2003 among Harry
L. Bradley, Jr. Partition Trust, Harry L. Bradley,
Jr. Trust, Jane Bradley Uihlien Pettit Partition
Trust, Jane Bradley Uihlien Trust, TCW Asset
Management Company and Trust Company of the West, a
California trust company, as Sub-CustodianBy:Name:Title:By:Name:Title:TCW ASSET MANAGEMENT COMPANY, a California
corporation, as Investment Manager under the Amended
and Restated Investment Management and Custody
Agreement dated as of March 18, 2004 among ING Life
Insurance and Annuity Company, TCW Asset Management
Company and Trust Company of the West, a California
trust company, as Sub-CustodianBy:Name:Title:By:Name:Title: [Signature Page to First Amendment to  Note Purchase Agreement]




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CONSENT AND REAFFIRMATION
  RIO VISTA ECO LLCBy:Ian BothwellManagerRIO VISTA GO LLCBy:Ian BothwellManagerGO, LLCBy:Ian BothwellManagerMV PIPELINE COMPANYBy:Ian BothwellPresident [Signature Page to First Amendment to  Note Purchase Agreement]




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RIO VISTA OPERATING LLCBy:Ian BothwellManagerRIO VISTA ENERGY PARTNERS L.P.By:
    Rio Vista GP LLC, its general partnerBy:Ian BothwellManager [Signature Page to First Amendment to  Note Purchase Agreement]




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Rio Vista
Fixed price Sales Contracts
 Counterparty: Clearwater Enterprises, L.L.C.
 Contract
    
    
    ContractConfirmation
    
    
    
    
    
    
    
    
    
    Quantity
    
    
    PriceNumber
    
    Begin
    
    
    End
    
    
    (mmbtu/mo)
    
    
    ($/mmbtu)
    
    
    Pipeline
    
    Delivery Point/Index Point28727
    
    
    4/1/2008
    
    
    
    10/31/2008
    
    
    
    30,000
    
    
    
    6.35
    
    
    Oneok Gas Transmission
    
    MV/OGT (R900)31601
    
    
    11/1/2008
    
    
    
    3/31/2009
    
    
    
    30,000
    
    
    
    8.61
    
    
    Oneok Gas Transmission
    
    MV/OGT (R900)31595 & 31956
    
    
    4/1/2008
    
    
    
    10/31/2008
    
    
    
    15,000
    
    
    
    7.97
    
    
    NA
    
    Swap: Inside Ferc Centerpoint East31597 & 31958
    
    
    11/1/2008
    
    
    
    3/31/2009
    
    
    
    15,000
    
    
    
    8.61
    
    
    NA
    
    Swap: Inside Ferc Centerpoint East
 [Schedule I   First Amendment to Note Purchase Agreement]




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HOLDERS SCHEDULE
 Allocation
    
    
    
    
    
    
    MaximumNote Holder
    
    %
    
    
    Commitment
    
    
    Credit AmountTCW Energy Fund X-NL,
L.P., a California
limited partnership
    
    
    23.03872
    %
    
    $
    5,702,083.20
    
    
    $
    6,911,616TCW Energy Fund XB-NL,
L.P., a California
limited partnership
    
    
    28.62534
    %
    
    $
    7,084,771.65
    
    
    $
    8,587,602TCW Energy Fund XC-NL,
L.P., a California
limited partnership
    
    
    9.48725
    %
    
    $
    2,348,094.38
    
    
    $
    2,846,175TCW Energy Fund XD-NL,
L.P., a California
limited partnership
    
    
    21.12823
    %
    
    $
    5,229,236.93
    
    
    $
    6,338,469Trust Company of the
West as Sub-Custodian
under the Amended and
Restated Investment
Management and Custody
Agreement dated as of
December 3, 2003 among
Ensign Peak Advisors,
Inc., TCW Asset
Management Company and
Trust Company of the
West
    
    
    6.81556
    %
    
    $
    1,686,851.10
    
    
    $
    2,044,668ING Life Insurance and
Annuity Company
    
    
    6.81556
    %
    
    $
    1,686,851.10
    
    
    $
    2,044,668Trust Company of the
West as Sub-Custodian
under the Amended and
Restated Investment
Management and Custody
Agreement dated as of
December 11, 2003 among
Harry L. Bradley, Jr.
Partition Trust, Harry
L. Bradley, Jr. Trust,
Jane Bradley Uihlien
Pettit Partition Trust,
Jane Bradley Uihlien
Trust, TCW Asset
Management Company and
Trust Company of the
West
    
    
    4.08934
    %
    
    $
    1,012,111.64
    
    
    $
    1,226,802Total
    
    
    100.00000
    %
    
    $
    24,750,000.00
    
    
    $
    30,000,000
 [Schedule 4  First Amendment to  Note Purchase Agreement]




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APPROVED PLAN OF DEVELOPMENT
 [Schedule 6  First Amendment to  Note Purchase Agreement]




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CLOSING CERTIFICATE
 CLOSING CERTIFICATE
  THE UNDERSIGNED HEREBY CERTIFIES AS FOLLOWS:
 Company
 Note Purchase Agreement First
Amendment Amendment Date Original Certificate
   a.
    
    all representations and warranties made by any Person in any Note
Document are true in all respects on and as of the date hereof, except to the
extent that such representation or warranty was made as of a specific date or
updated, modified or supplemented as of a subsequent date with the consent of
Required Holders and Administrative Agent;b.
    
    each Restricted Person and Parent have performed and complied with all
agreements and conditions required in the Note Documents to be performed or
complied with prior to the date hereof;c.
    
    as of the Amendment Date, no event has occurred and is continuing or
would result from the consummation of the borrowing contemplated on the date hereof
that would constitute an Event of Default or a Default (other than the Designated
Defaults defined and described in the First Amendment, which are being waived
pursuant to the provisions of Section 2.8 of the First Amendment);




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d.
    
    attached as Exhibit A to the Original Certificate is a true, correct
and complete copy of the Articles of Organization of Company as in effect on the
date hereof, certified by the Secretary of State of the State of Oklahoma;e.
    
    attached as Exhibit B to the Original Certificate is a true, correct
and complete copy of the Operating Agreement of Company as in effect on the date
hereof;f.
    
    attached as Exhibit D to the Original Certificate is a true, correct
and complete copy of certain resolutions duly adopted by unanimous written consent
of the sole Manager of Company in accordance with Companys Articles of
Organization and Operating Agreement and none of such resolutions has been
rescinded, revoked, modified, or amended in any respect, and all of such
resolutions are in full force and effect on the date hereof;g.
    
    Paragraph 6 of the Original Certificate contains a list of certain duly
elected, qualified and acting officers of Company. Each such person holds on the
date hereof the office set forth opposite such officers name in such Paragraph 6,
and the signature appearing in such Paragraph 6 opposite such officers name is
such officers genuine signature. Each such officer is duly authorized to execute
and deliver Transaction Documents on behalf of Company;h.
    
    as of the Amendment Date no Restricted Person has any Deposit Account
that is not subject to a control agreement in form and substance satisfactory to
Administrative Agent as required by Section 7.17 of the Note Purchase Agreement.
 [ Remainder of page intentionally left blank. Signature page follows. ]




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By:Ian BothwellManager [Closing Certificate]