Okla. Stat. tit. 26 § 12-119
Except as otherwise provided by law, an incumbent in any elective office for which a vacancy is filled by special election called by the Governor may file with the Oklahoma Secretary of State an irrevocable resignation in writing which states that the resignation will not become effective immediately, but rather will become effective on some date certain. Upon receipt of the irrevocable letter of resignation, the Governor shall set the date for the special election. The person elected at the special election shall take office on the later of the date of certification of the results of the special election or the date the resignation of the incumbent becomes effective and shall serve the remainder of the unexpired term.
Okla. Stat. tit. 26, § 12-119