Okla. Stat. tit. 68, § 2358.5

A. Interest on local governmental obligations issued after the effective date of this act for purposes other than to provide financing for projects for nonprofit corporations shall be exempt from Oklahoma income taxation. For these purposes, local governmental obligations shall include bonds or notes issued by, or on behalf of, or for the benefit of Oklahoma educational institutions, cities, towns, or counties or by public trusts of which any of the foregoing is a beneficiary. B. Interest on governmental obligations issued by the Oklahoma Department of Transportation after the effective date of this act for purposes of highway construction and maintenance shall be exempt from Oklahoma income taxation.