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                                  FORM 10-K/A-1

                       SECURITIES AND EXCHANGE COMMISSION
                              WASHINGTON, DC 20549
                              --------------------

              [X] ANNUAL REPORT PURSUANT TO SECTION 13 OR 15(d) OF
               THE SECURITIES EXCHANGE ACT OF 1934 [FEE REQUIRED]

                     FOR THE FISCAL YEAR ENDED MAY 31, 1999

                                       OR

                 [ ]TRANSITION REPORT PURSUANT TO SECTION 13 OR
                  15(d) OF THE SECURITIES EXCHANGE ACT OF 1934
                                [NO FEE REQUIRED]
                 FOR THE TRANSITION PERIOD FROM ______ TO ______

                         COMMISSION FILE NUMBER 1-13402

                               INPUT/OUTPUT, INC.
             (EXACT NAME OF REGISTRANT AS SPECIFIED IN ITS CHARTER)

             DELAWARE                                         22-2286646
(STATE OR OTHER JURISDICTION OF                            (I.R.S. EMPLOYER
 INCORPORATION OR ORGANIZATION)                            IDENTIFICATION NO.)

11104 WEST AIRPORT BLVD., STAFFORD, TEXAS                        77477
(ADDRESS OF PRINCIPAL EXECUTIVE OFFICES)                       (ZIP CODE)

       REGISTRANT'S TELEPHONE NUMBER, INCLUDING AREA CODE: (281) 933-3339

         SECURITIES REGISTERED PURSUANT TO SECTION 12(b) OF THE ACT:
COMMON STOCK, $0.01 PAR VALUE                   NEW YORK STOCK EXCHANGE
PREFERRED STOCK PURCHASE RIGHTS                 NEW YORK STOCK EXCHANGE
         (TITLE OF CLASS)            (NAME OF EACH EXCHANGE ON WHICH REGISTERED)

           SECURITIES REGISTERED PURSUANT TO SECTION 12(g) OF THE ACT:
                                      NONE

Indicate by check mark whether the registrant (1) has filed all reports required
to be filed by Section 13 or 15(d) of the Securities Exchange Act of 1934 during
the preceding 12 months (or for such shorter period that the registrant was
required to file such reports), and (2) has been subject to such filing
requirements for the past 90 days. Yes: [X] No: [ ]

Indicate by check mark if disclosure of delinquent filers pursuant to Item 405
of Regulation S-K is not contained herein, and will not be contained, to the
best of registrant's knowledge, in definitive proxy or information statements
incorporated by reference in Part III of this Form 10-K or any amendment to this
Form 10-K. [ ]

Aggregate market value of the voting and non-voting common equity held by
non-affiliates of the registrant at June 30, 1999 (for purposes of the
below-stated amount only, all directors, officers and 5% or more stockholders
are presumed to be affiliates):
                                  $287,235,000

Indicate the number of shares outstanding of the registrant's classes of Common
Stock, as of the latest practicable date.

       TITLE OF EACH CLASS                         NUMBER OF SHARES OUTSTANDING
        OF COMMON STOCK                                   AT JUNE 30, 1999
        ---------------                                   ----------------
       COMMON STOCK, $0.01 PAR VALUE                         50,663,858

                       DOCUMENTS INCORPORATED BY REFERENCE

Portions of the definitive Proxy Statement for the Registrant's 1999 Annual
Meeting of Stockholders are incorporated by reference into Part III hereof.

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                                     PART IV

ITEM 14. EXHIBITS, FINANCIAL STATEMENT SCHEDULES AND REPORTS ON FORM 8-K:

         (3)  Exhibits:

                  23.1     - Consent of KPMG LLP

                  99.1     - Information, Financial Statements and Exhibits
                             required by Form 11-K for the Input/Output, Inc.
                             Employee Stock Purchase Plan




                                   SIGNATURES



        The undersigned registrant hereby amends the following items, financial
statements and exhibits of its Annual Report for its fiscal year ended May 31,
1999 on Form 10-K as set forth in the pages attached hereto:

        To file as Exhibit 99.1 the Information, Financial Statements and
Exhibits required by Form 11-K for the Input/Output, Inc. Employee Stock
Purchase Plan.

        Pursuant to the requirements of Section 13 or 15(d) of the Securities
Exchange Act of 1934, the Registrant has duly caused this Form 10-K/A-1 report
to be signed on its behalf by the undersigned, thereunto duly authorized in the
city of Stafford, State of Texas, on October 28, 1999.

                                           Input/Output, Inc.


                                           /s/ Sam K. Smith
                                           ---------------------------------
                                           Director and
                                           Chief Executive Officer




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