Okla. Stat. tit. 19, § 545

All work issued out of the district court shall be served by the sheriff or his salaried deputies, together with such other work as may be placed in the hands of the sheriff or salaried deputies, by any court in his or their county except as provided in Section 158.1 of Title 12 of the Oklahoma Statutes. All process placed in the hands of the said sheriff shall be served promptly and the return thereof made without delay and filed in the proper court. A failure to promptly serve process placed in the hands of the sheriff, or the failure to perform expeditiously all the duties of his office, shall be grounds for removal of such sheriff.