Okla. Stat. tit. 23, § 23-6: Interest upon damages

Any person who is entitled to recover damages certain, or

capable of being made certain by calculation, and the right to

recover which is vested in him upon a particular day, is entitled

also to recover interest thereon from that day, except during such

time as the debtor is prevented by law, or by the act of the

creditor from paying the debt.