ORS § 116.313
Unless the will, or a revocable trust of which the decedent is settlor, otherwise provides, the tax shall be apportioned among all persons interested in the estate. The apportionment shall be made in the proportion that the value of the interest of each person interested in the estate bears to the total value of the interests of all persons interested in the estate. The values used in determining the tax shall be used for that purpose. In the event the decedent's will or revocable trust directs a method of apportionment of tax different from the method described in ORS 116.303 to 116.383, the method described in the will or revocable trust shall control. A mere testamentary direction to pay debts, charges, taxes or expenses of administration shall not be considered a direction against apportionment of estate taxes.
ORS 116.313