Okla. Stat. tit. 19 § 1220
Districts formed hereunder shall be exempt from all excise taxes 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 securities and evidences of indebtedness issued by a district created pursuant to the Ambulance Service Districts Act and the income interest and capital gains thereon shall not be subject to the income tax laws of this state and persons owning or holding the 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 securities and evidences of indebtedness.
Okla. Stat. tit. 19, § 1220