<PAGE>
 
                              
                           SHERIDAN ENERGY, INC.     
 
                   PROXY FOR SPECIAL MEETING OF STOCKHOLDERS
                                 JUNE 12, 1997
          THIS PROXY IS SOLICITED ON BEHALF OF THE BOARD OF DIRECTORS
   
  The undersigned hereby appoints Jeffrey E. Susskind and Michael A. Gerlich,
and each of them, attorneys and agents with full power of substitution to vote
all shares of voting stock of Sheridan Energy, Inc., which the undersigned
would be entitled to vote if personally present at the Meeting of Stockholders
of Sheridan Energy, Inc., to be held at the Four Seasons Hotel, 1300 Lamar
Street, in Houston, Texas, on June 12, 1997 and at any adjournment thereof, as
follows:     
 
  If properly executed, this proxy will be voted as directed on the reverse
side.
 
  IF NO DIRECTION IS INDICATED WITH RESPECT TO THE PROPOSALS ON THE REVERSE
SIDE, THIS PROXY WILL BE VOTED "FOR" ITEMS 1, 2 AND 3.
 
          THE BOARD OF DIRECTORS RECOMMENDS A VOTE "FOR" ITEMS 1 AND 2
 
    IMPORTANT: PLEASE SIGN, DATE AND RETURN THIS PROXY CARD PROMPTLY IN THE
                               ENCLOSED ENVELOPE!
 
                         (TO BE SIGNED ON REVERSE SIDE)
 
                                                                  SEE REVERSE
                                                                     SIDE
 
                
 X PLEASE MARK
   YOUR VOTES
   AS IN
   THIS EXAMPLE.
 
                    FOR      WITHHOLD   Nominees: Mr. Jonathan P. Carroll
1. Election of      [ ]        [ ]                Mr. Michael A. Gerlich   
   Directors                                      Mr. David H. Scheiber
                                                  Mr. Jeffrey E. Susskind
 
Instructions: To withhold authority to vote for an individual nominee, write
that nominee's name on the line provided below.
 
-----------------------------------                                 

                                                FOR      AGAINST     ABSTAIN
                                                                    
2. Approval of the Flexible Incentive Plan      [ ]        [ ]         [ ]
                                                                    
3. In their discretion with respect to          [ ]        [ ]         [ ] 
   (1) any other matters as may properly
   come before the meeting and any adjournment
   thereof, (2) approval of the minutes of the 
   prior meeting, if such approval does not
   amount to ratification of the action 
   taken at that meeting, (3) the election of
   any other person as a director if a 
   nominee named above is unable to serve or
   for good cause will not serve, and (4) 
   matters incident to the conduct of 
   the meeting. 

 
 
SIGNATURE(S) __________________________________________________  DATE ____, 1997
 
NOTE: Please sign exactly as name appears hereon. Joint owners should each
      sign. Executors, administrators, trustees, etc., should indicate the
      capacity in which signing.
<PAGE>
 
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                                TGX CORPORATION
 
                   PROXY FOR SPECIAL MEETING OF STOCKHOLDERS
                                 JUNE 12, 1997
          THIS PROXY IS SOLICITED ON BEHALF OF THE BOARD OF DIRECTORS
 
  The undersigned hereby appoints Jeffrey E. Susskind and Michael A. Gerlich,
and each of them, attorneys and agents with full power of substitution to vote
all shares of voting stock of TGX Corporation, which the undersigned would be
entitled to vote if personally present at the Meeting of Stockholders of TGX
Corporation, to be held at the Four Seasons Hotel, 1300 Lamar Street, in
Houston, Texas, at 9:00 a.m. Houston time, on June 12, 1997 and at any
adjournment thereof, as follows:
 
  If properly executed, this proxy will be voted as directed on the reverse
side.
 
  IF NO DIRECTION IS INDICATED WITH RESPECT TO THE PROPOSALS ON THE REVERSE
SIDE, THIS PROXY WILL BE VOTED "FOR" ITEMS 1, 2 AND 3.
 
          THE BOARD OF DIRECTORS RECOMMENDS A VOTE "FOR" ITEMS 1 AND 2
 
    IMPORTANT: PLEASE SIGN, DATE AND RETURN THIS PROXY CARD PROMPTLY IN THE
                               ENCLOSED ENVELOPE!
 
                         (TO BE SIGNED ON REVERSE SIDE)
 
                                                                  SEE REVERSE
                                                                     SIDE

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X  PLEASE MARK
   YOUR VOTES
   AS IN
   THIS EXAMPLE.
     
                      FOR       WITHHOLD    NOMINEES: Mr. Jonathan P. Carroll
1. Election of        [ ]         [ ]                 Mr. Michael A. Gerlich 
   Directors                                          Mr. David H. Scheiber  
                                                      Mr. Jeffrey E. Susskind
     
                                             
Instructions: To withhold authority to vote for an individual nominee, write 
that nominee's name on the line provided below.                              
                                                                             
-----------------------------------                                           

                                              FOR       AGAINST       ABSTAIN
2. Approval of the proposed merger            [ ]         [ ]           [ ]  
   of the Company                                                  
                                                            
3. In their discretion with respect to        [ ]         [ ]           [ ]  
   (1) any other matters as may properly
   come before the meeting and any 
   adjournment thereof, (2) approval of 
   the minutes of the prior meeting, if 
   such approval does not amount to 
   ratification of the action taken at 
   that meeting, (3) the election of any 
   other person as a director if a nominee 
   named above is unable to serve or for 
   good cause will not serve, and (4) 
   matters incident to the conduct of 
   the meeting.

 
SIGNATURE(S) ______________________________________________DATE _______, 1997
 
NOTE: Please sign exactly as name appears hereon. Joint owners should each
      sign. Executors, administrators, trustees, etc., should indicate the
      capacity in which signing.

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