Okla. Stat. tit. 60 § 755
Unless otherwise provided in the nontestamentary instrument creating the interest with reference to the possibility of a disclaimer by the beneficiary, the interest disclaimed shall be distributed or otherwise be disposed of in the same manner as if the disclaimant had died immediately preceding the death or other event which causes him to become finally ascertained as a beneficiary and his interest to become indefeasibly fixed both in quality and quantity and, in any case, the disclaimer shall relate for all purposes to that date, whether filed before or after such death or other event. However, one disclaiming an interest in a nonresiduary gift under a trust instrument or otherwise shall not be excluded, unless his disclaimer so provides, from sharing in a gift of the residue even though, through lapse, such residue includes the assets disclaimed. If the disclaimer pertains to a joint tenancy interest in property, the interest disclaimed shall be distributed or otherwise be disposed of in the same manner as if the disclaimant had died immediately preceding the death of the other person having a joint tenancy interest in the same property whose death most closely preceded the effective date of the disclaimer or, if no person having a joint tenancy interest has died, then as if the disclaimant never owned the joint tenancy interest which was disclaimed.
Okla. Stat. tit. 60, § 755