Okla. Stat. tit. 11 § 32-114
The levy and assessment shall be payable in not more than ten equal annual installments. Interest on the whole amount remaining due and unpaid each year shall be at a rate not exceeding eight percent (8%) per annum. Delinquent installments, and the unpaid interest thereon, shall draw interest at the rate of twelve percent
(12%) per annum from maturity until paid. Any owner of land within the improvement district may, within thirty (30) days after the assessing ordinance is passed, pay the entire amount assessed against such land. The assessing ordinance may provide that if the entire amount of all assessments shall not have been paid within thirty (30) days after passage of the assessing ordinance, special assessment bonds may be issued, sold, collected and enforced as to unpaid installments of assessments in the same manner as bonds for municipal street improvements are issued, sold, collected and enforced.
Okla. Stat. tit. 11, § 32-114