Okla. Stat. tit. 12, § 2607
The credibility of a witness may be attacked by any party, including the party calling the witness.
Laws 1978, SB 276, c. 285, § 607, eff. October 1, 1978; Amended by Laws 2002, HB 1939, c. 468, § 46, eff. November 1, 2002 (superseded document available).