Okla. Stat. tit. 19, § 19-863.16: Existing nonconforming uses

The lawful use of a building, structure or premises as such

existed at the time of the adoption and recording of any regulation

affecting it, may be continued, although such use does not conform

with the provisions of such regulation. The board, as it affects

its jurisdiction, may provide for the termination of nonconforming

uses either by specifying the period or periods within which they

shall be required to cease, or by providing a formula or formulas

whereby the compulsory termination of nonconforming use shall be so

fixed as to allow a reasonable period for the recovery of

amortization of the investment in the nonconformance, provided, that

in each instance any such action of the board shall be taken only

after public notice and hearing thereon has been had before the

commission and that commission's recommendations with respect

thereto certified to the board.