Okla. Stat. tit. 19 § 891
The cost and expense of purchasing and acquiring property and constructing the works and improvements herein provided for shall be wholly paid in cash or in the bonds of said district issued as hereinbefore provided at their par value with accrued interest. The bonds may be issued in series or installments, and shall be turned over and delivered to the contractor in payment of the amount due in accordance with the terms of his contract, including advertising, engineering, and other expenses. Said bonds shall be executed and delivered from time to time on completion and approval of the work or any part thereof, to an amount equal to the cost and expense of purchasing and acquiring property and constructing the works and improvements so completed and accepted. Such bonds or any portion thereof may be sold for cash at not less than par and accrued interest, within the discretion of the board of directors.
Okla. Stat. tit. 19, § 891