Okla. Stat. tit. 62 § 426a
Any municipality may refund any part or all of its bonded and judgment indebtedness and the interest thereon, by agreement with holders of such indebtedness to be funded or refunded, by issuance of funding or refunding bonds maturing within twenty-five (25) years from date. When any such funding or refunding bonds mature other than serially they shall be optional and subject to redemption on any interest-paying date. Said bonds shall be designated optional funding or refunding bonds, and shall recite that they are subject to redemption at any interest-paying date. Said bonds shall be authorized, executed, registered and approved in the same manner as funding and refunding bonds issued under other statutes in force. Provided, however, that no funding or refunding bonds issued hereunder shall bear a higher rate of interest than the indebtedness which is funded or refunded.
It shall be the duty of the treasurer and governing board of any municipality issuing funding or refunding bonds under the provisions of this act to request tenders from all known holders of such bonds at least thirty (30) days prior to each interest paying date. The form of such call for tenders setting out the time and place and other particulars shall be prescribed by the Attorney General. The said treasurer and governing board are hereby directed to purchase any bonds which may have been offered at less than par, provided preference must be given to the purchase of bonds which are offered for the least money. Provided further that if no bonds are offered at less than par, then it shall be the duty of the treasurer and governing board to call by lot at par and accrued interest as many of the bonds as he may have funds on hand for that purpose and that interest on said bonds so called shall cease within sixty (60) days after said call is made. All tenders of bonds and all drawing of bonds by lot shall be performed in a public meeting of the governing board. Provided sufficient money is retained in the sinking fund to pay the next two succeeding semiannual interest payments coming due on each bond.
Okla. Stat. tit. 62, § 426a