Okla. Stat. tit. 25, § 221
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.
Laws 1961, HB 657, p. 240, § 1, emerg. eff. March 21, 1961; Amended by Laws 1977, SB 25, c. 217, § 1.