EXHIBIT 5.1

                           Fulbright & Jaworski L.L.P.
                   A Registered Limited Liability Partnership
                            1301 McKinney, Suite 5100
                            Houston, Texas 77010-3095
                                www.fulbright.com

Telephone: (713) 651-5151                              Facsimile: (713) 651-5246
                                  July 16, 2004

Input/Output, Inc.
12300 Parc Crest Drive
Stafford, Texas 77477

Gentlemen:

We have acted as counsel for Input/Output, Inc., a Delaware corporation (the
"Registrant"), in connection with the registration under the Securities Act of
1933, as amended, of 365,000 shares of the Registrant's common stock, $0.01 par
value per share (the "Shares"), which are to be issued pursuant to the
Input/Output, Inc.-Concept Systems Employment Inducement Stock Option Program
(the "Program"), evidenced by stock option award agreements entered into between
the Registrant and the individual participants in the Program.

In connection therewith, we have reviewed the relevant corporate resolutions of
the Company and have examined originals or copies, certified or otherwise
identified to our satisfaction, of such corporate records and documents as we
have deemed necessary as a basis for the opinions hereinafter expressed. We also
have examined the Registrant's Registration Statement on Form S-8 (the
"Registration Statement") to be filed with the Securities and Exchange
Commission with respect to the Shares.

We have assumed the authenticity and completeness of all records, certificates
and other instruments submitted to us as originals, the conformity to original
documents of all records, certificates and other instruments submitted to us as
copies, the authenticity and completeness of the originals of those records,
certificates and other instruments submitted to us as copies and the correctness
of all statements of fact contained in all records, certificates and other
instruments that we have examined.

Based on the foregoing, and having regard for such legal considerations as we
have deemed relevant, we are of the opinion that the Shares have been duly and
validly authorized for issuance and, when issued in accordance with the terms of
their stock option award agreements, will be validly issued, fully paid and
non-assessable.

The opinions expressed herein relate solely to, are based solely upon and are
limited exclusively to the laws of the State of Texas, the federal laws of the
United States of America, and the General Corporation Law of the State of
Delaware, as amended, to the extent applicable.

We hereby consent to the filing of this opinion as an exhibit to the
Registration Statement.



                                                                     EXHIBIT 5.1

                                                 Very truly yours,

                                                 /s/ FULBRIGHT & JAWORSKI L.L.P.

                                                 Fulbright & Jaworski L.L.P.