Okla. Admin. Code § 590:25-9-11
The payment, method of payment and any distribution options shall be available in accordance with the benefit payment elections as set forth on the appropriate distribution request form. If the Participant elects to receive a deferred payout, the date selected for payouts to begin may be changed upon written notice to the Plan Administrator prior to the previously selected payout date subject to any applicable minimum distribution requirements. The method of payment may be changed upon written notice to the Plan Administrator. A Participant electing to commence distribution shall have the opportunity to designate the extent to which the distribution should be taken in whole or in part from Pre-Tax Elective Deferrals or the Participant's other subaccounts, as applicable. In the absence of such designation, the distribution shall be taken pro rata from the subaccounts within the Participant's Account.
Okla. Admin. Code § 590:25-9-11