Okla. Stat. tit. 12A, § 12A-4A-506: Rate of interest

RATE OF INTEREST

(a) If, under this Article, a receiving bank is obliged to pay

interest with respect to a payment order issued to the bank, the

amount payable may be determined (i) by agreement of the sender and

receiving bank, or (ii) by a funds-transfer system rule if the

payment order is transmitted through a funds-transfer system.

(b) If the amount of interest is not determined by an agreement

or rule as stated in subsection (a) of this section, the amount is

calculated by multiplying the applicable Federal Funds rate by the

amount on which interest is payable, and then multiplying the

product by the number of days for which interest is payable. The

applicable Federal Funds rate is the average of the Federal Funds

rates published by the Federal Reserve Bank of New York for each of

the days for which interest is payable divided by three hundred

sixty (360). The Federal Funds rate for any day on which a

published rate is not available is the same as the published rate

for the next preceding day for which there is a published rate. If

a receiving bank that accepted a payment order is required to refund

payment to the sender of the order because the funds transfer was

not completed, but the failure to complete was not due to any fault

by the bank, the interest payable is reduced by a percentage equal

to the reserve requirement on deposits of the receiving bank.