ORS § 319.290
Applications for refunds made under ORS 319.280, 319.320 and 319.330 must be filed with the Department of Transportation before the expiration of 15 months from the date of purchase or invoice, except that unused fuel reported as an ending inventory on any claim may be included in a subsequent claim if presented not later than 15 months from the filing date of the claim which established the inventory. All applications for refunds based upon exportation of motor vehicle fuel from this state in the fuel supply tank of a motor vehicle must be filed with the department before the expiration of 15 months from the last day of the month in which the fuel was used, or before the expiration of 15 months from the date of an assessment for unpaid tax by the state in which the fuel was used.
ORS 319.290