Okla. Stat. tit. 18, § 18-381.38: Classification of deposit accounts

Any association may classify its deposit accounts according to

the character, amount or duration thereof, or regularity of

additions thereto, and may pay additional or higher rates of

earnings on accounts based on such classifications than is paid on

regular deposit accounts, provided that any such higher rate, or

bonus, to be paid on any class of accounts shall not exceed the

limitations prescribed by the State Banking Commissioner or by

applicable federal regulations. A mutual association may also

classify its accounts according to type of account, such as full

paid, single payment, installment, optional installment, bonus or

other types of accounts designated by the bylaws and permitted by

the Commissioner.