ORS § 307.050
Whenever real and personal property of the United States or any department or agency of the United States is the subject of a contract of sale or other agreement whereby on certain payments being made the legal title is or may be acquired by any person and that person uses and possesses the property or has the right of present use and possession, then a real market value for the property shall be determined, as required under ORS 308.232, without deduction on account of any part of the purchase price or other sum due on such property remaining unpaid. The property shall have an assessed value determined under ORS 308.146 and shall be subject to tax on the assessed value so determined. The lien for the tax shall neither attach to, impair, nor be enforced against any interest of the United States in the real or personal property. This section does not apply to real or personal property held and in immediate use and occupation by this state or any county, municipal corporation or political subdivision of this state, or to standing timber, prior to severance, of the United States or any department or agency of the United States that is the subject of a contract of sale or other agreement.
ORS 307.050