Oregon Revised Statutes Probate Law § 118.165

(1) At any time within three years after the date that an estate tax return is filed, the Department of Revenue may give notice of deficiency as prescribed in ORS 305.265.

(2) If the department finds that the value of the gross estate has been undervalued on the estate tax return by an amount greater than 25 percent, notice of deficiency may given at any time within five years after the date that the return is filed.

(3) The limitations to the giving of notice of a deficiency provided in this section do not apply to a deficiency resulting from a false or fraudulent estate tax return or in a case where no return has been filed.