Okla. Stat. tit. 14A, § 14A-3-203.1: Credit to finance medical goods and services -

Contract for delinquency charges.

With respect to a revolving loan account or other similar

arrangement which may be used by the debtor exclusively for the

purpose of obtaining credit to finance medical goods and services,

the parties may contract for a delinquency charge on any installment

not paid in full within ten (10) days after its scheduled due date

in an amount, not exceeding the greater of: Five Dollars ($5.00) or

five percent (5%) of the unpaid amount of the installment. For

purposes of this section, the term "installment" shall mean, with

respect to a revolving loan account, the minimum periodic payment

required to be made by the debtor under the terms of the account

agreement between the lender and the debtor.