Okla. Stat. tit. 60, § 299.3

A donee may exercise a power of appointment only by an instrument executed with sufficient formalities to pass title to the property covered by the power. When a power of appointment is exercisable only by will, a donee may not exercise it by deed. When a power of appointment is exercisable by deed, a donee may exercise it by will. Laws 1977, c. 210, § 3.