The general usury rate for consumer loans is 21% under the Oklahoma UCCC (See Title 14A, section 3-508A of the Oklahoma Statutes). This section also allows lenders to charge interest under an alternate tiered structure as follows:

30% on principal balance up to $1,230
21% on principal balance between $1,230 and $4,100
15% on principal balance over $4,100

Note: the principal balance tiers reflect the adjusted numbers as of July 1, 2006, as set by the Oklahoma Department of Consumer Credit. Using the tiered rates will result in a blended rate over 21% on loans under $9,000. For reference here is a Rate Chart provided by American Bank Systems.

For non-consumer loans the maximum rate is 45%. See 14A O.S. sections 3-605 and 5-107.2.