EXHIBIT 5.1

                                  June 10, 2004
Input/Output, Inc.
12300 Parc Crest Dr.
Stafford, Texas 77477

     Re:    Input/Output, Inc. Registration Statement on Form S-8; GX Technology
            Corporation Employee Stock Option Plan

Gentlemen:

         We have acted as counsel to Input/Output, Inc., a Delaware corporation
(the "Company"), in connection with the preparation for filing with the
Securities and Exchange Commission of a Registration Statement on Form S-8 (the
"Registration Statement") under the Securities Act of 1933, as amended. The
Registration Statement relates to the registration of 2,963,225 shares (the
"Shares") of the Company's common stock, par value $0.01 per share (the "Common
Stock"), issuable pursuant to the GX Technology Corporation Employee Stock
Option Plan (the "Plan").

         We have examined the Plan and such corporate records, documents,
instruments and certificates of the Company, and have reviewed such questions of
law as we have deemed necessary, relevant or appropriate to enable us to render
the opinion expressed herein. In such examination, we have assumed without
independent investigation the authenticity of all documents submitted to us as
originals, the genuineness of all signatures, the legal capacity of all natural
persons, and the conformity of any documents submitted to us as copies to their
respective originals. As to certain questions of fact material to this opinion,
we have relied without independent investigation upon statements or certificates
of public officials and officers of the Company.

         Based upon such examination and review, we are of the opinion that the
Shares have been duly and validly authorized and will, upon issuance and
delivery as contemplated by the Plan, be validly issued, fully paid and
nonassessable outstanding shares of Common Stock.

         This Firm consents to the filing of this opinion as an exhibit to the
Registration Statement.

                                                    Very truly yours,

                                                    /s/ PORTER & HEDGES, L.L.P.

                                                    PORTER & HEDGES, L.L.P.