Okla. Stat. tit. 11 § 32-113
The portion of the cost of any improvement to be assessed against the property in the improvement district shall be apportioned against the property in accordance with the special benefits accruing thereto by reason of the improvement. The cost may be assessed equally per front foot or per square foot against all lots and pieces of land within the improvement district or the cost may be determined and fixed on the basis of any other reasonable assessment plan which will result in imposing substantially equal burdens or shares of the cost upon property similarly benefited. The governing body shall determine the final apportionment of costs of the improvement and shall levy, by ordinance, assessments in accordance with the apportionment against the property liable therefor. No suit shall be maintained in any court to enjoin or in any way contest the validity of any special assessment for the cost of acquiring or improving parking stations unless the same be instituted and summons served within thirty (30) days after the date of the publication of the ordinance levying the assessment.
Okla. Stat. tit. 11, § 32-113