Exhibit 10.20


 


WEINMAN GEOSCIENCE, INC.


17103 PRESTON ROAD, SUITE
200


DALLAS, TEXAS 75248


 


June 15, 2009


 


Global Geophysical Services, Inc.


3535 Briarpark Drive, Suite 200


Houston, Texas 77042


 


Re:                               Subordinated
Promissory Note dated as of December 10, 2008, as amended by Letter
Agreement dated May 5, 2009 (as further amended, supplemented or otherwise
modified, the “Note”), by and among GLOBAL
GEOPHYSICAL SERVICES, INC., a Delaware corporation (“Maker”),
and WEINMAN GEOSCIENCE, INC., a Texas corporation (“Payee”)


Gentlemen:


 


Reference is made to the
Note.  Terms that are defined in the Note
and not otherwise defined herein are used herein with the meanings given them
in the Note.


 


Maker has requested that
Payee extend the required payment of principal and part of the required payment
of accrued interest that are due and payable on June 15, 2009 and that the
Payee accept a prepayment of the required payments of principal that are due on
December 1, 2009 and December 1, 2010.  Accordingly, Maker and Payee hereby agree
that:


 


1.  The payment in respect of the Notes due and
payable on June 15, 2009 is hereby extended as follows:


 


(a)           $900,000 of principal and the accrued interest on that
amount, shall be due and payable on September 1, 2009, together with
interest accruing on such amount from June 15, 2009 through the time of
payment;


 


(b)           $900,000 of principal and the accrued interest on that
amount, shall be due and payable on July 1, 2009, together with interest
accruing on such amount from June 15, 2009 through the time of payment;
and


 


(c)           The remainder of the amount otherwise payable on June 15,
2009 has been paid by Maker and received by Payee.


 


2.  Consistent with Section 2.5 of the Note
(which permits prepayments of principal and interest at any time) and Section 4.3
of the Note (which provides that prepayments made in Permitted Junior
Securities do not violate the subordination provisions of the Notes), Maker is


 

















 


delivering on the date
hereof, and Payee hereby accepts, 295,809 shares of Series A Convertible
Preferred Stock, par value $0.01 per share, of Maker as a prepayment in full of
the scheduled payments due under the Note on December 1, 2009 and December 1,
2010.


 


In order to induce Payee to
enter into this Letter, Maker represents and warrants to Payee that as of the
date of this Letter, no Blockage Default or Senior Indebtedness Acceleration
has occurred and is continuing and no Standstill Period is in effect.


 


The Note is hereby ratified
and confirmed in all respects.  Except as
expressly set forth above, the execution, delivery and effectiveness of this
Letter shall not operate as a waiver of any right, power or remedy of Maker or
Payee under the Note, nor constitute a waiver of any provision of the Note.


 


THIS LETTER AND THE RIGHTS AND OBLIGATIONS OF THE
PARTIES HEREUNDER SHALL BE GOVERNED BY, AND SHALL BE CONSTRUED AND ENFORCED IN
ACCORDANCE WITH, THE LAWS OF THE STATE OF TEXAS.


 


This Letter may be executed
in any number of counterparts, each of which when so executed and delivered
shall be deemed an original, but all such counterparts together shall
constitute but one and the same instrument.


 


Please execute a counterpart
of this Letter in the place provided below to evidence your agreement to the
foregoing and your continuing ratification of the Note in consideration hereof,
whereupon this Letter shall become effective as of the date first written
above.


 


	
   

  	
  Yours
  truly,

  
	
   

  	
   

  
	
   

  	
  WEINMAN GEOSCIENCE, INC.

  
	
   

  	
   

  	
   

  
	
   

  	
   

  	
   

  
	
   

  	
  By:

  	
   

  
	
   

  	
   

  	
  Name:

  
	
   

  	
   

  	
  Title:

  
	
   

  	
   

  	
   

  
	
   

  	
   

  	
   

  
	
   

  	
  Accepted
  and agreed to as of the date first written above:

  
	
   

  	
   

  	
   

  
	
   

  	
   

  	
   

  
	
   

  	
  GLOBAL GEOPHYSICAL
  SERVICES, INC.

  
	
   

  	
   

  	
   

  
	
   

  	
   

  	
   

  
	
   

  	
  By:

  	
   

  
	
   

  	
   

  	
  Name:  P. Matthew Verghese

  
	
   

  	
   

  	
  Title:  Senior Vice President &

  
	
   

  	
   

  	
    Chief
  Financial Officer

  



 


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