Okla. Stat. tit. 12 § 1148.5A
If, in the exercise of reasonable diligence, service cannot be made upon the defendant personally nor upon any person residing upon the premises over fifteen (15) years of age, then in lieu of service by certified mail, service may be obtained for the sole purpose of adjudicating the right to restitution of the premises by the sheriff's posting or by private process service posting of said summons conspicuously on the building on the premises, and, if there be no building on said premises, then by posting the same at some conspicuous place on the premises sought to be recovered at least five (5) days prior to the date of trial, and by the claimant's mailing a copy of said summons to the last-known address of the defendant by certified mail at least five (5) days prior to said date of trial. Such service shall confer no jurisdiction upon the court to render any judgment against the defendant for the payment of money nor for any relief other than the restoration of possession of the premises to the claimant, unless the defendant appears at trial. If the court only renders a judgment for restoration of possession of the premises, the claimant shall not be precluded from pursuing a subsequent action for the payment of rent. A judgment for forcible entry and detainer shall not preclude the property owner from pursuing a subsequent action for other monetary relief. Such service shall not be rendered ineffectual by the failure of the defendant to actually see or receive such posted process nor by the failure of the defendant to actually receive or sign a return receipt for such mailed process.
Okla. Stat. tit. 12, § 1148.5A