Okla. Stat. tit. 60 § 125
It shall be the duty of the Attorney General or the district attorney of the county where the land is situated, when he or she shall be informed or have reason to believe that any lands in the state are being held contrary to the provisions of Section 121 et seq. of this title, or the provisions of the Constitution of this state, to institute suit in behalf of this state in the district court of the county in which such lands are situated, praying for the foreclosure of the same . Provided, that before any such suit is instituted, the Attorney General, or district attorney aforesaid, as the case may be, shall give thirty (30) days' notice by registered letter of his or her intention to sue, directed to the owner of the lands, at his or her last-known post office address or to the persons who last rendered the same for taxes, or to any known agents of the owner; proof of having mailed such registered letter shall be deemed and held prima facie evidence of the giving of such notice.
Okla. Stat. tit. 60, § 125