Okla. Stat. tit. 70 § 17-116.16
Effective July 1, 2000, a member of the Teachers' Retirement System of Oklahoma who was employed in an adjunct position in an institution under The Oklahoma State System of Higher Education prior to becoming a member of the System, may purchase a maximum of five (5) years of credit for such employment, pursuant to this section. One (1) year of service credit may be purchased for any school year in which the member worked eighteen (18) credit hours or more in such an adjunct position. The purchase of service credit shall be made pursuant to Section 17-116.8 of Title 70 of the Oklahoma Statutes and shall be considered contributing service for purposes of vesting and retirement. The Board of Trustees shall promulgate such rules as are necessary to implement the provisions of this section.
Okla. Stat. tit. 70, § 17-116.16