Okla. Stat. tit. 82 § 1274
Districts formed hereunder shall be exempt from all excise taxes of whatsoever kind or nature, and further, shall be exempt from payment of assessments in any general or special taxing district levied upon the property of the district, whether real, personal or mixed. Any and all obligations, securities and evidences of indebtedness issued by a district formed pursuant to this act shall be exempt from all inheritance or death taxes, and the income interest and capital gains thereon shall not be subject to the income tax laws of this state. Persons owning or holding the obligations, securities and evidences of indebtedness or their heirs, devisees, successors or assigns shall not be required to pay to the State of Oklahoma income tax upon the profits and capital gains upon the obligations, securities and evidences of indebtedness.
Okla. Stat. tit. 82, § 1274