Okla. Stat. tit. 11 § 11-111
When a vacancy occurs in the office of mayor, the vice-mayor shall act as mayor until a mayor is elected by the council and qualified for office. To fill the vacancy, the council shall elect a registered voter of the city, who may or may not already be a council member at the time, to be mayor until the next general municipal election, and to serve until a successor is elected and qualified. Any vacancy shall then be filled at the next general municipal election by election of a person to complete the balance of any unexpired term. If the vacancy has not been filled within sixty (60) days after it occurs, the governing body shall call for a special election for the purpose of filling the vacancy for the duration of the unexpired term. However, if less than one (1) year remains of the unexpired term, the council shall elect a registered voter of the city, who may or may not already be a council member at the time, to be mayor for the duration of the unexpired term. When a vacancy occurs in the office of vice-mayor, the council shall elect from among its members another vice-mayor for the duration of the unexpired term.
Okla. Stat. tit. 11, § 11-111