EXHIBIT 5.1



                    (FULBRIGHT & JAWORSKI L.L.P. LETTERHEAD)



January 27, 2004



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

Ladies and Gentlemen:

     We have acted as counsel to Input/Output, Inc., a Delaware corporation (the
"Company") in connection with the registration under the Securities Act of 1933,
as amended, of $60,000,000 principal amount of the Company's 5.50% Convertible
Senior Notes due 2008 (the "Notes"), and 13,888,890 shares of the Company's
common stock, par value $.01 per share, which are issuable on conversion of the
Notes (the "Shares"), as described in the Company's Registration Statement on
Form S-3 to be filed with the Securities and Exchange Commission with respect to
the Notes and the Shares (the "Registration Statement").

     In connection with the foregoing, we have examined originals or copies of
such corporate records, as applicable, of the Company, certificates and other
communications of public officials, certificates of officers of the Company and
such other documents as we have deemed necessary for the purpose of rendering
the opinions expressed herein. As to questions of fact material to those
opinions, we have, to the extent we deemed appropriate, relied on certificates
of officers of the Company and on certificates and other communications of
public officials. We have assumed the genuineness of all signatures on, and the
authenticity of, all documents submitted to us as originals, the conformity to
authentic original documents of all documents submitted to us as copies, the due
authorization, execution and delivery by the parties thereto of all documents
examined by us, and the legal capacity of each individual who signed any of
those documents.

     Based upon the foregoing, and having due regard for such legal
considerations as we deem relevant, we are of the opinion that the Notes have
been validly issued and the Shares, when issued on conversion of Notes in
accordance with the terms of the Notes and that certain Indenture dated as of
December 10, 2003 (the "Indenture"), between the Company and The Bank of New
York Trust Company of Florida, N.A., as trustee, will be duly and validly
issued, fully paid and nonassessable.

     The opinions expressed herein are limited exclusively to the federal laws
of the United States of America, the laws of the State of New York and
applicable provisions of, respectively, the Delaware Constitution, the Delaware
General Corporation Law and reported judicial interpretations of such law, and
we are expressing no opinion as to the effect of the laws of any other
jurisdiction.




Input/Output, Inc.
January 27, 2004
Page 2

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


                                               Very truly yours,



                                               /s/ Fulbright & Jaworski L.L.P.