Exhibit 10.20
 AGREEMENT AND AMENDMENT NO. 3
  RECITALS
    Section 1. Defined Terms; Other Provisions .
 Section 2. Agreement  Borrowing Base




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Section 3. Amendments to Credit Agreement
 Applicable Margin Maturity Date
  Applicable Margin  means (i) with respect to any Advance, (a) during any
time when an Event of Default under Section 7. 01(a) or Section 7. 01(e) exists, 3%
per annum plus the rate per annum set forth in the pricing grid set forth below for
the relevant Type of such Advance based on the present Utilization Level applicable
at such time, (b) during any time when any other Event of Default exists and upon
election by the Required Lenders (or the Administrative Agent at the direction of
the Required Lenders), 3% per annum plus the rate per annum set forth in the pricing
grid set forth below for the relevant Type of such Advance based on the present
Utilization Level applicable at such time, and (c) at any other time, the rate per
annum set forth in the pricing grid set forth below for the relevant Type of such
Advance based on the relevant Utilization Level applicable at such time, and (ii)
with respect to the commitment fees, the rate per annum set forth in the pricing
grid set forth below based on the relevant Utilization Level applicable at such
time. The Applicable Margin for any Advance and the commitment fees shall change
when and as the relevant Utilization Level changes.
 Applicable MarginBorrowing BaseUtilization
    
    Eurodollar Rate 
Advance

    
    Reference Rate 
Advance

    
    Commitment 
FeeLess than 50%
    
    
    2.00
    %
    
    
    1.00
    %
    
    
    0.375
    %Greater than or equal to 50% but less than 75%
    
    
    2.25
    %
    
    
    1.25
    %
    
    
    0.500
    %Greater than or equal to 75% but less than 90%
    
    
    2.50
    %
    
    
    1.50
    %
    
    
    0.500
    %Greater than or equal to 90%
    
    
    2.75
    %
    
    
    1.75
    %
    
    
    0.500
    %
  Maturity Date  means May 23, 2016.
 Additional Subordinated Debt
 (vi) a scheduled maturity date that is earlier than May 23, 2017,
 ) the issuance of Senior Unsecured Notes each issuance of Senior Unsecured Notes
  Commitment Fees . The Borrower agrees to pay to the
Administrative Agent for the account of each Lender having a Commitment a commitment
fee in an amount equal to the Applicable Margin on the daily Unused Commitment
Amount of such Lender, from the date of this Agreement until the Commitment
Termination Date; provided that, no commitment fee shall accrue on the Commitment of
a Defaulting Lender during the
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period such Lender remains a Defaulting Lender. The
commitment fees shall be due and payable quarterly in arrears on the last day of
each March, June, September, and December commencing on June 30, 2010 and continuing thereafter through and including
the Commitment Termination Date.
  (p) Liens not otherwise permitted in this Section 6.01 so long as (i) such Liens do
not encumber Oil and Gas Properties and (ii) the aggregate amount of obligations
secured thereby shall not exceed $1,000,000.
  (j) Senior Unsecured Notes and the guaranties given by Restricted Subsidiaries with
respect thereto; provided that (i) the principal amount of such Debt shall not
exceed $700,000,000 in the aggregate, (ii) the Borrowing Base is reduced if and to
the extent required by Section 2. 02(e) , and (iii) the Debt Incurrence Proceeds
thereof shall be applied to make the payments, if any, required under Section
2. 05(b)(ii) ;
 Investments
 (f) other investments, loans or advances not otherwise permitted by this Section
6.06 in an aggregate amount not to exceed $10,000,000 at any time.
 Section 4. Representations and Warranties .
 Section 5. Conditions to Effectiveness .
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Section 6. Acknowledgments and Agreements .
      Section 7. Reaffirmation of the Guaranty
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Section 8. Flood Insurance Regulations . Flood Insurance Regulations
 Section 9. Counterparts .
 Section 10. Successors and Assigns .
 Section 11. Invalidity .
 Section 12. Governing Law .
 Section 13. Entire Agreement .
 THERE ARE NO UNWRITTEN ORAL AGREEMENTS AMONG THE PARTIES.
 [SIGNATURES BEGIN ON NEXT PAGE]
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BORROWER:
    
    ALTA MESA HOLDINGS, LPBy:
    
    Alta Mesa Holdings GP, LLCits general partnerBy:
    
    /s/ Michael A. McCabeName:
    
    Michael McCabeTitle:
    
    Chief Financial OfficerGUARANTORS:
    
    ALTA MESA FINANCE SERVICES CORP.ALTA MESA GP, LLCARI DEVELOPMENT, LLCALTA MESA ACQUISITION SUB, LLCBRAYTON MANAGEMENT GP, LLCBRAYTON MANAGEMENT GP II, LLCCAIRN ENERGY USA, LLCLOUISIANA ONSHORE PROPERTIES LLCTHE MERIDIAN PRODUCTION, LLCTHE MERIDIAN RESOURCE, LLCTHE MERIDIAN RESOURCE & EXPLORATION LLCTMR DRILLING, LLCVIRGINIA OIL AND GAS, LLCALTA MESA HOLDINGS GP, LLCALTA MESA ENERGY LLCEach by:
    
    /s/ Michael A. McCabeMichael A. McCabeChief Financial OfficerALTA MESA SERVICES, LPARANSAS RESOURCES, LPBUCKEYE PRODUCTION COMPANY, LPLOUISIANA EXPLORATION & ACQUISITIONS, LPNAVASOTA RESOURCES, LTD., LLPNUECES RESOURCES, LPOKLAHOMA ENERGY ACQUISITIONS, LPTEXAS ENERGY ACQUISITIONS, LPGALVESTON BAY RESOURCES, LPPETRO ACQUISITIONS, LPPETRO OPERATING COMPANY, LPORION OPERATING COMPANY, LPEach by: Alta Mesa GP, LLCBy:
    
    /s/ Michael A. McCabeMichael A. McCabeChief Financial Officer




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BRAYTON RESOURCES, LP,By: Brayton Management GP, LLC, its general partnerBy:
    
    /s/ Michael A. McCabeMichael A. McCabeChief Financial OfficerBRAYTON RESOURCES II, L.P.,By: Brayton Management
GP II, LLC, its general partnerBy:
    
    /s/ Michael A. McCabeMichael A. McCabeChief Financial OfficerALTA MESA RESOURCES, LP,By:
    
    Alta Mesa Resources GP, LLC,its sole general partnerBy:
    
    /s/ Michael A. McCabeMichael A. McCabe,Chief Financial OfficerPETRO ACQUISITIONS HOLDINGS, LP,By:
    
    Petro Acquisitions Holdings GP, LLC,its sole general partnerBy:
    
    /s/ Michael A. McCabeMichael A. McCabe,Chief Financial OfficerPETRO OPERATING COMPANY HOLDINGS, INC.,By:
    
    
    
    /s/ Michael A. McCabeMichael A. McCabeChief Financial OfficerGALVESTON BAY RESOURCES HOLDINGS, LP,By:
    
    Galveston Bay Resources Holdings GP, LLCits sole general partnerBy:
    
    /s/ Michael A. McCabeMichael A. McCabe,Chief Financial Officer




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ADMINISTRATIVE AGENT/ISSUING LENDER/LENDER:
    
    WELLS FARGO BANK, N.A.By:
    
    /s/ Shiloh DavilaShiloh DavilaVice President




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LENDER:
    
    UNION BANK, N.A.By:
    

/s/
Brian CaddellName:
    

Brian CaddellTitle:
    

Assistant
Vice President




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LENDER:
    
    TORONTO DOMINION (NEW YORK) LLCBy:
    
    /s/ Bebi YasinName:
    
    Bebi YasinTitle:
    
    Authorized Signatory




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LENDER:
    
    ING CAPITAL LLCBy:
    
    /s/ Charles
HallName:
    

Charles
HallTitle:
    
    Managing
Director




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LENDER:
    
    CITIBANK, N.A.By:
    
    /s/ Thomas BenavidesName:
    
    Thomas BenavidesTitle:
    
    Senior Vice President




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LENDER:
    
    CAPITAL ONE, NATIONAL ASSOCIATIONBy:
    
    /s/ Nancy M. MakName:
    
    Nancy M. MakTitle:
    
    Vice President




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LENDER:
    
    BOKF, NA DBA BANK OF TEXASBy:
    
    /s/ Martin W. WilsonName:
    
    Martin W. WilsonTitle:
    
    Senior Vice President




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LENDER:
    
    AMEGY BANK NATIONAL ASSOCIATIONBy:
    

/s/
Mark SericeName:
    

Mark
SericeTitle:
    

Senior
Vice President




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LENDER:
    
    TEXAS CAPITAL BANK, N.A.By:
    

/s/
W. David McCarver IVName:
    

W. David McCarver IVTitle:
    

Vice
President




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ANNEX I  BORROWING BASE AS OF MAY 23, 2011*
 PRO RATA SHARE OF THE
    
    PERCENTAGE OFLENDERS
    
    BORROWING BASE*
    
    TOTALWells Fargo Bank, N.A.
    
    $
    63,859,649.12
    
    
    
    24.561403509
    %Union Bank, N.A.
    
    $
    41,052,631.58
    
    
    
    15.789473684
    %Toronto Dominion (New York) LLC
    
    $
    31,017,543.86
    
    
    
    11.929824561
    %ING Capital LLC
    
    $
    25,543,859.65
    
    
    
    9.824561404
    %Citibank, N.A.
    
    $
    25,543,859.65
    
    
    
    9.824561404
    %Capital One, N.A.
    
    $
    22,807,017.54
    
    
    
    8.771929824
    %Bank of Texas, NA
    
    $
    22,807,017.54
    
    
    
    8.771929824
    %Amegy Bank National Association
    
    $
    13,684,210.53
    
    
    
    5.263157895
    %Texas Capital Bank, N.A.
    
    $
    13,684,210.53
    
    
    
    5.263157895
    %TOTAL
    
    $
    260,000,000.00
    
    
    
    100
    %
 
 *
    
    Borrowing Base is subject to redetermination pursuant to the terms of the Credit Agreement, as
amended.