Exhibit 10.01

FOURTH AMENDMENT TO PROMISSORY NOTE

RECITALS

WHEREAS, the undersigned five corporate entities (each, a "Maker;” or
collectively, “Makers”) were each co-makers of a certain Promissory Note (the
“Note”) dated June 1, 2010, in the original stated amount of $6,987,646.00, in
favor of Teton, Ltd., a Texas limited partnership (“Payee”);

WHEREAS, the Note was previously amended by Amendment to Note dated October 1,
2010 (the “First Amendment”), to eliminate the requirement for an interest
payment to be made on October 1, 2010;

WHEREAS, the Note was also amended by Second Amendment to Note dated January 1,
2011 (the “Second Amendment”), to eliminate the requirement for an interest
payment to be made on January 1, 2011;

WHEREAS, the Note was also amended by Third Amendment to Promissory Note dated
April 1, 2011 (the “Third Amendment”), to (i) eliminate the requirement for
an  interest payment to be made on April 1, 2011, and (ii) extend the maturity
date of the Note from June 1, 2011, to June 1, 2013;

WHEREAS, in conjunction with Pegasi Energy Resources Corporation’s engagement of
Beaufort International Associates Limited on an exclusive basis to raise funds
for the company (the “Beaufort Engagement”), Makers have requested, and Payee
has agreed under certain terms set forth herein, to further amend the Note to
extend the maturity date of the Note from June 1, 2013, to June 1, 2015;

NOW, THEREFORE, in consideration of the premises and the mutual promises
contained in this Fourth Amendment to Promissory Note (the “Fourth Amendment”),
Makers and Payee hereby agree as follows:

AGREEMENT

1.           Amendment to Note.  The Note is hereby amended to extend the
maturity date of the Note from June 1, 2013, to June 1, 2015.  As a result of
this amendment, all outstanding principal and accrued interest from the date of
the Note shall be payable on the final maturity date of the Note.

2.           Added Event of Default.  By written notice to Pegasi Energy
Resources Corporation, a Nevada corporation f/n/a Maple Mountain Explorations
Inc. (“PERC”), Payee may at its option declare a default on the Note if PERC
does not raise funds for the company during or as a result of the Beaufort
Engagement.  In such event, Payee may accelerate the Note and exercise all
remedies for a default on the Note.
 
 
 
 
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3.           Makers are responsible for all costs incurred by Payee, including
without limit reasonable attorneys’ fees, with regard to the preparation and
execution of this Fourth Amendment.

4.           The execution of this Fourth Amendment shall not be deemed to be a
waiver of any Default or Event of Default.

5.           All the terms used in this Fourth Amendment which are defined in
the Note shall have the same meaning as used in the Note, unless otherwise
defined in this Fourth Amendment.  All the terms used in this Fourth Amendment
which are defined in the Stock Pledge Agreement shall have the same meaning as
used in the Stock Pledge Agreement, unless otherwise defined in this Fourth
Amendment.

6.           Makers waive, discharge, and forever release Payee, Payee's
employees, officers, directors, attorneys, stockholders, and their successors
and assigns, from and of any and all claims, causes of action, allegations or
assertions that Makers have or may have had at any time up through and including
the date of this Fourth Amendment, against any or all of the foregoing,
regardless of whether any such claims, causes of action, allegations or
assertions are known to Makers or whether any such claims, causes of action,
allegations or assertions arose as  result of Payee's actions or omissions in
connection with the Note, or any amendments, extensions or modifications
thereof, or Payee's administration of the debt evidenced by the Note or
otherwise, INCLUDING ANY CLAIMS, CAUSES OF ACTION, ALLEGATIONS OR ASSERTIONS
RESULTING FROM PAYEE’S OWN NEGLIGENCE, except and to the extent (but only to the
extent) caused by Payee’s gross negligence or willful misconduct.

7.           This Fourth Amendment is not an agreement to any further or other
amendment of the Note.

8.           Makers expressly acknowledge and agree that except as expressly
amended in this Fourth Amendment, the Note remains in full force and effect and
is ratified and confirmed.  This Fourth Amendment shall neither extinguish nor
constitute a novation of the Note or indebtedness evidenced thereby.

9.           The parties covenant and agree as follows:

(1)       The rights and obligations of the parties shall be determined solely
from the written “Loan Agreement” (as such term is defined in Section
26.02(a)(2) of the Texas Business and Commerce Code) executed and delivered in
connection with the Loan, and any oral agreements between or among the parties
are superseded by and merged into the Loan Agreement.

(2)       The Loan Agreement has not been and may not be varied by any oral
agreements or discussions that have or may occur before, contemporaneously with,
or subsequent thereto.
 
 
 
 
 
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(3)       THE WRITTEN LOAN AGREEMENT REPRESENTS 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 AMONG THE PARTIES.

Executed to be effective as of June 23, 2011.
 
Makers:
 
Payee:
 
       
Pegasi Energy Resources Corporation,
 
Teton, Ltd., a Texas limited partnership
 
a Nevada corporation f/n/a
 
By: Notet Corp., a Texas corporation,
 
Maple Mountain Explorations Inc.
 
its general partner
                 
By:
 
By:  
 
Richard Lindermanis, Senior Vice President
 
W.L. Sudderth, Secretary
 
and CFO
             
Pegasi Energy Resources Corporation,
     
a Texas corporation (and wholly-owned
     
subsidiary of Pegasi Energy Resources Corporation,
     
a Nevada corporation f/n/a Maple Mountain Explorations Inc.)
                     
By:
     
Richard Lindermanis, Vice President
             
Pegasi Operating Inc., a Texas corporation (and wholly-owned
     
subsidiary of Pegasi Energy Resources Corporation,
     
a Texas corporation)
                     
By:
     
Richard Lindermanis, Vice President
             
TR Rodessa, Inc., a Texas corporation (and wholly-owned
     
subsidiary of Pegasi Energy Resources Corporation,
     
a Texas corporation)
                     
By:
     
Richard Lindermanis, Vice President
             
59 Disposal, Inc., a Texas corporation (and wholly-owned
     
subsidiary of Pegasi Energy Resources Corporation,
     
a Texas corporation)
              By:      
Richard Lindermanis, Vice President
             

 
 
 
 
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