Okla. Admin. Code § 715:10-5-27
Out-of-state service performed after the last year of Oklahoma membership service shall not qualify as out-of-state credit. A member who returns to Oklahoma public education employment after working out-of-state shall purchase that out-of-state service in the same manner as a new member of TRS: i.e., the member must have two (2) years of Oklahoma service after the out-of-state service for each year of out-of-state service purchased. No out-of-state service or salaries shall be utilized for the calculation of a member's final average salary at retirement. No out-of-state service can be used to meet the minimum requirement of five (5) full years of employment in the public schools of Oklahoma to qualify for vesting and retirement benefits.
Okla. Admin. Code § 715:10-5-27