Okla. Stat. tit. 62 § 424
The governing body, or authority of any county, city, town, township, board of education, school district or other municipal corporation, issuing refunding bonds under authority of this act, shall provide, prior to the delivery of said refunding bonds, for a levy of annual taxes on all taxable property in the county, city, town, township, board of education, school district, or other municipal corporations, as the case may be, sufficient in amount to pay, and for the express purpose of paying, the interest on said bonds as it falls due, and also to pay and discharge the principal thereof at maturity; and, in every instance in which any county, city, town, township, board of education, school district or other municipal corporation shall issue bonds under this act, it shall be the imperative duty of the proper officers, whose duty it may be to levy taxes, to annually levy, at the time of making the levy of other taxes, a tax sufficient in amount to pay the interest upon said bonds and the coupons as they become due, and to create a sinking fund for the payment of the principal of such bonds at their maturity.
Okla. Stat. tit. 62, § 424