FIRST AMENDMENT TO RIGHTS AGREEMENT 
                       BY AND BETWEEN INPUT/OUTPUT, INC.
              AND HARRIS TRUST AND SAVINGS BANK AS RIGHTS AGENT


     This First Amendment to Rights Agreement ("First Amendment"), dated 
effective as of April 21, 1999, evidences the amendment of that certain 
Rights Agreement (herein so called) by and between Input/Output, Inc. (the 
"Company") and Harris Trust and Savings Bank as Rights Agent dated as of 
January 17, 1997.

                                    RECITALS

     WHEREAS, Section 27 of the Rights Agreement provides that the Board of 
Directors of the Company may from time to time supplement or amend the Rights 
Agreement in such manner as the Board of Directors deems necessary or 
desirable; and 

     WHEREAS, the Company and SCF-IV, L.P., a Delaware limited partnership, 
intend to enter into that certain Purchase Agreement (the "Purchase 
Agreement") pursuant to which the Company will, among other things, issue 
shares of its Series B Preferred Stock, and upon exercise of an option by 
SCF-IV, L.P. as provided for therein, shares of its Series C Preferred Stock, 
each of which is convertible into the Company's Common Stock; and

     WHEREAS, the Board of Directors of the Company has approved this First 
Amendment by action taken at a meeting duly held on April 21, 1999;

     NOW, THEREFORE, for and in consideration of the premises and the mutual 
agreements herein set forth, the parties hereby agree, at the direction of 
the Company, as follows:

     1.   Section 1(a) of the Rights Agreement is hereby amended to modify the
definition of "Acquiring Person" by adding a sentence to the end of such
definition to read as follows:

     "Notwithstanding any provision to the contrary contained herein,
     neither SCF nor any of its Affiliates shall be deemed to be an
     Acquiring Person as a result of any combination of the following
     actions: (i) the execution and delivery of the Purchase Agreement,
     (ii) the acquisition of shares of Series B Preferred Stock and/or
     Series C Preferred Stock of the Company in accordance with the terms
     of the Purchase Agreement, (iii) the acquisition of shares of Common
     Stock of the Company upon conversion of the shares of Series B
     Preferred Stock or Series C Preferred Stock, (iv) the acquisition  of
     securities of the Company in accordance with the terms of Section 5.11 



     of the Purchase Agreement (including any Common Stock issuable upon
     conversion, exercise or exchange thereof), or (v) an acquisition of
     additional shares of Common Stock of the Company to the extent
     permitted by the terms of Section 5.12(a) of the Purchase Agreement."

     2.   Section 1 of the Rights Agreement shall be further revised by 
adding the following additional definitions thereto:

     "PURCHASE AGREEMENT" shall mean that certain Purchase Agreement to be 
entered into by and between SCF and the Company.

     "SCF" shall mean SCF-IV, L.P., a Delaware limited partnership.

     "SERIES B PREFERRED STOCK" shall mean the Company's Series B Preferred 
Stock, $.01 par value per share, to be issued pursuant to the terms of the 
Purchase Agreement.

     "SERIES C PREFERRED STOCK" shall mean the Company's Series C Preferred 
Stock, $.01 par value per share, which may be issued pursuant to the terms of 
the Purchase Agreement.

     3.   The first sentence of Section 3(a) of the Rights Agreement is 
hereby amended by adding the following sentence following the end of such 
sentence:

     "PROVIDED HOWEVER, that in no event shall a Stock Acquisition Date or
     a Distribution Date be deemed to occur as a result of (i) the
     execution and delivery of the Purchase Agreement by SCF and the
     Company, (ii) the acquisition by SCF of shares of Series B Preferred
     Stock and/or  Series C Preferred Stock of the Company in accordance
     with the terms of the Purchase Agreement, (iii) the acquisition by SCF
     of shares of Common Stock of the Company upon conversion of the shares
     of Series B Preferred Stock or Series C Preferred Stock, (iv) the
     acquisition by SCF of securities of the Company in accordance with the
     terms of Section 5.11 of the Purchase Agreement (including any Common
     Stock issuable upon conversion, exercise or exchange thereof), or (v)
     the acquisition by SCF of additional shares of Common Stock of the
     Company to the extent permitted by the terms of Section 5.12(a) of the
     Purchase Agreement."

     4.   This First Amendment shall be deemed to be a contract made under the
laws of the State of Delaware and for all purposes shall be governed by and
construed in accordance with the laws of the State of Delaware applicable to
contracts to be made and performed entirely within the State of Delaware.


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     5.   This First Amendment may be executed in any number of counterparts 
and each of such counterparts shall for all purposes be deemed to be an 
original, and all such counterparts shall together constitute but one and the 
same instrument.

     6.   Except to the extent expressly amended by the First Amendment, the 
Rights Agreement shall remain in full force and effect.

     IN WITNESS WHEREOF, the parties hereto have caused this Agreement to be 
duly executed and attested, all as of the day and year first above written.


                                        INPUT/OUTPUT, INC.

Attest:

By: /s/ Chris Wolfe                     By: /s/ W.J. Zeringue              
    -------------------------------         -------------------------------
Title: Vice President                   Title: Chief Executive Officer     
       ----------------------------            ----------------------------


                                        HARRIS TRUST AND SAVINGS BANK,
                                        as Rights Agent

Attest:

By: /s/ Lorraine Rodewald               By: /s/ Ray Rosenbaum              
    -------------------------------         -------------------------------

Title: Assistant Vice President         Title: Vice President              
       ----------------------------            ----------------------------


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