Okla. Stat. tit. 12, § 2703
The facts or data in the particular case upon which an expert bases an opinion or inference may be those perceived by or made known to the expert at or before the hearing. If of a type reasonably relied upon by experts in the particular field in forming opinions or inferences upon the subject, the facts or data need not be admissible in evidence in order for the opinion or inference to be admitted.
Laws 1978, SB 276, c. 285, § 703, eff. October 1, 1978; Amended by Laws 2002, HB 1939, c. 468, § 55, eff. November 1, 2002 (superseded document available).