Okla. Stat. tit. 46, § 1

Every instrument purporting to be an absolute or qualified conveyance of real estate or any interest therein, but intended to be defeasible or as security for the payment of money, shall be deemed a mortgage and must be recorded and foreclosed as such either in an action to enforce the mortgage or pursuant to a power of sale as provided for in the Oklahoma Power of Sale Mortgage Foreclosure Act.