Exhibit 23.1


            CONSENT OF INDEPENDENT REGISTERED PUBLIC ACCOUNTING FIRM

We have issued our report dated February 22, 2005, accompanying the consolidated
financial statements and schedules included in the Annual Report of O. I.
Corporation on Form 10-K for the year ended December 31, 2004. We hereby consent
to the incorporation by reference of said report in the Registration Statements
of O. I. Corporation on Forms S-8 (File No. 33-24505, effective October 3, 1988,
File No. 33-62209, effective December 20, 1988, File No. 33-66822, effective
August 2, 1993 and File No. 333-106254, effective June 18, 2003).

GRANT THORNTON LLP

Houston, Texas
March 23, 2005