Okla. Stat. tit. 12, § 12-729.5

A. The money in which the parties to a transaction have agreed

that payment is to be made is the proper money of the claim for

payment.

B. If the parties to a transaction have not otherwise agreed,

the proper money of the claim, as in each case may be appropriate,

is the money:

1. Regularly used between the parties as a matter of usage or

course of dealing;

2. Used at the time of a transaction in international trade, by

trade usage or common practice, for valuing or settling transactions

in the particular commodity or service involved; or

3. In which the loss was ultimately felt or will be incurred by

the party claimant.