It shall be unlawful for any employer within the State of Oklahoma to willfully pay wages to women employees at a rate less than the rate at which he pays any employee of the opposite sex for comparable work on jobs which have comparable requirements relating to skill, effort and responsibility, except where such payment is made pursuant to a seniority system; a merit system; a system which measures earnings by quantity or quality of production; or a differential based on any factor other than sex.
Okla. Stat. tit. 40, § 198.1