Okla. Stat. tit. 62 § 421
Any county, city, town, township, board of education, school district, or any other municipal corporation in this state, whether operating under the provision of a special charter or otherwise, is hereby authorized and empowered to issue its bonds for the purpose of refunding bonded and/or coupons indebtedness, outstanding for more than two (2) years, and to issue new bonds with interest representing the rate of interest agreed upon, in payment for any amount of outstanding bonded and coupon indebtedness; which bonds may be exchanged pursuant to agreement with the holders of such indebtedness, or sold for not less than their par value, in the manner now or hereafter provided by law for the sale of other bonds of such municipalities, or any of them, and the proceeds of said sale applied to the redemption of the bonds to be refunded. If said bonds are offered for sale, and no legally accepted bids are received at said sale, the county, city, town, township, board of education, school district, or other municipal corporation issuing such refunding bonds, in its discretion, may either again offer such bonds for sale, or may exchange such refunding bonds, on a par for par basis, for the bonds, and interest, to be refunded; provided, however, if an agreement has been made for the exchange of such bonds the same shall be exchanged, as herein provided, without first having been offered for sale. Whether such refunding bonds are sold or exchanged, they shall be delivered only upon simultaneous surrender, payment and cancellation of a like amount of the bonds to be refunded, inclusive of the interest accrued thereon. Such refunding bonds may be issued in such amount, or amounts, that the par value thereof, plus accrued interest to date of delivery, shall equal, but not exceed, the par value of the bonds and/or coupons to be refunded to the date of the delivery and cancellation thereof. Said refunding bonds shall bear interest at any rate not exceeding the maximum rate provided by Section 498.1 of this title, and shall mature serially and in substantially equal installments, beginning not less than three (3) nor more than five (5) years after the date of said bonds; provided, however, that the last maturing installment may be for such sum less than two installments as will complete the full issue of such bonds, notwithstanding the necessity of varying the amount thereof to complete the same.
Okla. Stat. tit. 62, § 421