Oregon Revised Statutes Public Lands § 275.210

(1) A purchase agreement made pursuant to ORS 275.190 or 275.200 must be filed with the clerk, accountant or secretary, as the case may be, of the county in which the real property is situated.

(2) An assignment of a purchase agreement, or of an interest in the purchase agreement or of an interest in the property described in the purchase agreement, is not valid unless it is in writing, subscribed by the holder of the purchase agreement and filed with the county clerk of the county in which the land is situated.