Okla. Stat. tit. 25, § 25-221: Use of certified mail with return receipt requested in

place of registered mail.

It is hereby declared and directed that use of "certified United

States mail with return receipt requested," or "certified mail,"

"restricted delivery" shall be a full and complete legal compliance

with the statutes of Oklahoma permitting, directing, or requiring

use of "Registered United States mail" or "certified United States

mail" or "certified United States mail" a return receipt requested,

or "certified United States mail," "restricted delivery," or any

other such similar designations by any person in a public or private

capacity, and all provisions of the statutes of Oklahoma are hereby

modified to effect such change.