Okla. Stat. tit. 21, § 21-62.1: Imprisonment where no maximum

Whenever any person is declared punishable for a crime by

imprisonment in the penitentiary for a term not less than any

specified number of years, and no limit to the duration of such

imprisonment is declared, the court authorized to pronounce judgment

upon such conviction may, in its discretion, sentence such offender

to imprisonment during the natural life of the offender, or for any

number of years not less than such as are prescribed.