Okla. Stat. tit. 18, § 806

A professional entity may be formed for the purpose of rendering one specific type of professional service or related professional services and services ancillary thereto and shall not engage in any business other than rendering the professional service or services which it was organized to render and services ancillary thereto; provided, however, that a professional entity may own real and personal property necessary or appropriate for rendering the type of professional services it was organized to render and may invest its funds in real estate, mortgages, stocks, bonds and any other type of investments.