Oregon Revised Statutes Revenue and Taxation § 323.330

Unless the refund is one described in ORS 323.320, interest shall be computed, allowed and paid upon any overpayment for the purchase of stamps at the rate established under ORS 305.220 for each month or fraction of a month during a period beginning 45 days after the due date for payment of the purchase for which the overpayment was made or the date of the payment, whichever is the later, to the time the refund is made. No refund or credit shall be made of any interest imposed upon the claimant with respect to the amount being refunded or credited.