Okla. Stat. tit. 17, § 523

Nothing herein contained shall be construed to impair existing contractual rights nor shall it prohibit parties from contracting to establish correlative rights on the subject matter contained in this act. This act shall not be applicable to nor affect in any way property held by an Indian whose interest is restricted against voluntary or involuntary alienation under the laws of the United States or property held by an Indian tribe or by the United States for any Indian tribe.