Okla. Stat. tit. 18 § 381.43
Any association or federal association may accept deposit accounts in the name of any administrator, executor, conservator, guardian, trustee, or other fiduciary for a named beneficiary or beneficiaries. Any such fiduciary shall have power to vote as a member of a mutual association as if the membership were held absolutely, to open and to make additions to, and to withdraw such deposit account in whole or in part. The withdrawal value of any such deposit account, and earnings thereon, or other rights relating thereto may be paid or delivered, in whole or in part, to such fiduciary without regard to any notice to the contrary as long as such fiduciary is living. The payment or delivery to any such fiduciary or a receipt or acquittance signed by any such fiduciary to whom any such payment or any such delivery of rights is made shall be a valid and sufficient release and discharge of an association for the payment or delivery so made. Whenever a deposit account shall be opened by any person who designates himself or herself or another as trustee by written declaration of trust, which provides that the trust shall terminate upon the death of such person, then, in the event of the death of the person so described as trustee, the withdrawal value of such deposit account or any part thereof, together with the earnings thereon, may be paid to the person for whom the deposit account was thus described to have been opened. The payment or delivery to any such beneficiary, beneficiaries or designated person for any such payment or delivery shall be a valid and sufficient release and discharge of an association for the payment or delivery so made.
Okla. Stat. tit. 18, § 381.43