EXHIBIT 5.1


                         [CONNER & WINTERS LETTERHEAD]

                                 June 18, 2003

O.I. Corporation
151 Graham Road
Box 9010
College Station, Texas 77842-9010

      Re:   O.I. Corporation
            Registration Statement on Form S-8

Ladies and Gentlemen:

      We have acted as Oklahoma counsel for O.I. Corporation, an Oklahoma
corporation (the "Company"), in connection with the registration under the
Securities Act of 1933, as amended (the "Securities Act"), of an aggregate of
350,000 shares of the Company's Common Stock, $0.10 par value per share (the
"Shares"), issuable pursuant to the Company's 2003 Incentive Compensation Plan
(the "Plan"). A Registration Statement on Form S-8 (the "Registration
Statement") covering the issuance and sale of the Shares from time to time upon
exercise of stock options to be granted under the Plan has been filed under the
Securities Act with the Securities and Exchange Commission (the "Commission").

      In reaching the conclusions expressed in this opinion, we have (a)
examined such certificates of public officials and of corporate officers and
directors and such other documents and matters as we have deemed necessary or
appropriate, (b) relied upon the accuracy of facts and information set forth in
all such documents, and (c) assumed the genuineness of all signatures, the
authenticity of all documents submitted to us as originals, the conformity to
original documents of all documents submitted to us as copies, and the
authenticity of the originals from which all such copies were made. We have
assumed that the consideration to be received by the Company for each of the
Shares upon issuance will equal or exceed the par value per share of Common
Stock of the Company. We note that (i) the Company's Articles of Incorporation,
as amended, provide that the duration of the Company shall be fifty years and
(ii) the Company was originally incorporated in 1963. Accordingly, we have also
assumed that the Company will remain in existence at all times in which Shares
may be issued under the Plan.

      Based on the foregoing, we are of the opinion that the Shares have been
duly authorized and, when sold, issued and delivered in the manner and for the
consideration described in the Plan and applicable authorized forms of agreement
thereunder, will be validly issued, fully paid and nonassessable shares of
Common Stock of the Company.

O.I. Corporation
June 18, 2003
Page 2



      We are members of the bar of the State of Oklahoma. Our opinion expressed
above is limited to the laws of the State of Oklahoma, and we do not express any
opinion herein concerning the laws of any other jurisdiction.

      We consent to the filing of this opinion as an exhibit to the Registration
Statement. In giving this consent, we do not thereby admit that we are included
in the category of persons whose consent is required under Section 7 of the
Securities Act or the rules and regulations of the Commission.

                                    Yours very truly,

                                    CONNER & WINTERS, P.C.

                                    /s/ Conner & Winters, P.C.