Okla. Stat. tit. 62 § 395
When a refunding has been agreed upon, it shall be the duty of the proper officers to issue such bonds at the rate agreed upon, to the holder of such indebtedness, in the manner prescribed in this article; but no bonds shall be issued under this article until the proper evidence of the indebtedness for which the same are to be issued shall be delivered up for cancellation: Provided, that no bonded indebtedness shall be refunded by the board of county commissioners or any mayor and city council or any board of trustees of any town, township or any school district board, or board of education, under this article, except such as have been issued and outstanding at least two (2) years at the time of such refunding; and Provided, further, that except for the refunding of outstanding debt, including outstanding bonds and matured coupons thereof, or judgments thereon, or warrants, no bonds of any class or description shall hereafter be issued where the total bonded indebtedness of said county, city, town, township, school district or board of education would thereby exceed five percent (5%) of the assessment for taxation as shown by the last finding and determination by the proper board of equalization for state and county purposes.
Okla. Stat. tit. 62, § 395