Okla. Stat. tit. 11 § 29-203
Any municipality having a volunteer fire department shall limit by ordinance the size of the volunteer fire department to not less than twelve nor more than twenty-five members for municipalities with a population of more than one thousand five hundred (1,500); or not less than eight or more than twenty-five members for municipalities with a population of eight hundred (800) to one thousand five hundred (1,500); or not less than six or more than twenty-five members for municipalities with a population of less than eight hundred (800). Any municipality having a volunteer fire department that serves a nine-one-one (911) emergency telephone area of fifty (50) square miles or more may increase the size of the volunteer fire department up to an additional five members, with the total number of members of the volunteer fire department not to exceed thirty.
Okla. Stat. tit. 11, § 29-203