Okla. Stat. tit. 69 § 1320
Assessments in conformity to the appraisement and apportionment as corrected and confirmed by the governing body of the city or the board of county commissioners shall be payable, in cash, in ten equal installments, and shall bear interest at a rate not to exceed seven percent (7%) per annum until paid, payable in each year at such time as the several installments are made payable. The governing body of the city or the board of county commissioners shall by ordinance or resolution levy assessments in accordance with the appraisement and apportionment, as so confirmed, against the various tracts, pieces and parcels of land liable therefor, exclusive of streets and alleys. The ordinance or resolution shall provide that the owners of the property so assessed shall have the privilege of paying the amounts of their respective assessments without interest at any time within thirty (30) days from the date of the first publication of the ordinance or resolution.
Okla. Stat. tit. 69, § 1320