Okla. Stat. tit. 69, § 69-1323: Assessments - When payable

(a) The first installment of such assessment, together with

interest upon the whole assessment from the date of the passage of

the assessing ordinance or resolution to the first of the next

September, shall be due and payable on or before the 1st day of

September, next succeeding the passage of the ordinance or

resolution; provided, that if such assessing ordinance or resolution

is not passed prior to the 1st day of July, the first installment of

the assessment shall be due and payable with interest from the date

of passage to the 1st day of September of the following year.

(b) In case any installment or interest is not paid when due,

the unpaid installment and the unpaid interest thereon shall draw

interest at the rate of twelve percent (12%) per annum from maturity

until paid, except as hereinafter otherwise provided.

(c) With respect to assessments levied by any city, such

assessments and interest whether collected by the city or the county

treasurer shall be paid to the city treasurer, who shall keep the

same in a separate special fund for the purpose of paying the bonds

and interest coupons thereon issued against such assessments.

(d) With respect to assessments levied by any board of county

commissioners, the same shall be collected by the county treasurer

who shall keep the same in a separate special fund and shall

disburse the same in the payment of bonds and interest coupons

thereon issued against such assessments.

(e) After the payment of all bonds and interest thereon, any

surplus remaining in the fund shall be used by the city or the board

of county commissioners for the purpose of repairing or maintaining

the limited access facility and for no other purpose whatsoever.