Okla. Stat. tit. 5 § 9
Should the amount of the attorney's fees be agreed upon in the contract of employment, then such attorney's lien and cause of action against such adverse party shall be for the amount or portion of the property so agreed upon. If the fee be not fixed by contract the lien and cause of action, as aforesaid, shall be for a reasonable amount for not only the services actually rendered by such attorney, but for a sum, which it might be reasonably supposed, would have been earned by him, had he been permitted to complete his contract, and been successful in the action, and such attorney in order to recover need not establish that his client, if the case has gone to trial, would have been successful in the action, but the fact of settlement shall be sufficient without other proof to establish that the party making the settlement was liable in the action. Should the contract be for a contingent fee and specify the amount for which action is to be filed, then the lien and cause of action, as aforesaid shall be for the amount contracted for if fixed at a definite sum of money or for the percentage of the amount or property sued for as mentioned in said contract where the fee is fixed on a percentage basis, not exceeding thirty-three and one-third percent (33 1/3%) of the amount sued on where the settlement is before a verdict or judgment and if made after verdict or judgment then the full contract price.
Okla. Stat. tit. 5, § 9