Okla. Stat. tit. 11 § 37-210
The municipal body may contract for the services of special attorneys, auditors or consulting engineers to make the necessary surveys, and prepare plans, plats, profiles, estimates and all other details for the work of improvements and to supervise the work. Any such consulting engineer shall be a person, firm or corporation, resident in the State of Oklahoma, and duly registered as an engineer in the State of Oklahoma. A consulting engineer may be employed also to furnish the necessary advertising, printing, transcripts, legal fees, preparation of assessment rolls, and such other expense as may be necessary. The municipality shall provide for the payment of such services and expenses from the assessments to be levied as part of the cost of such improvments, except as otherwise provided.
Okla. Stat. tit. 11, § 37-210