Okla. Stat. tit. 60, § 60-35: Future estates

Subject to the rules of this chapter, a freehold estate, as well

as an estate for years, may be created to commence at a future day;

an estate for life may be created in a term of years, and a

remainder limited thereon; a remainder of a freehold or an estate

for years, either contingent or vested, may be created, expectant on

the determination of a term of years; and a fee may be limited on a

fee, upon a contingency, which if it should occur, must happen

within the period prescribed herein.