Okla. Stat. tit. 11 § 36-110
A municipal governing body may contract for the services of consulting engineers to prepare the necessary surveys, plans, plats, profiles, estimates and all other details for the work of improvements and to supervise the work. The consulting engineer may be a person, firm or corporation, resident in or outside the State of Oklahoma, duly registered as an engineer in the State of Oklahoma. The consulting engineer may be employed also to furnish the necessary advertising, printing, appraising, transcripts and other expense as may be necessary. The municipality shall provide for the payment of such services and expenses from the assessments to be levied against the abutting property as part of the cost of the improvement.
Okla. Stat. tit. 11, § 36-110