Oregon Revised Statutes Revenue and Taxation § 319.760

(1) If the Department of Transportation is not satisfied that a report filed or amount of tax or penalty paid to the state by any user or seller is correct, the department may assess the tax and penalty due based upon any information available to the department.

(2) If a seller fails to account satisfactorily for any fuel sold or disposed of, it shall be presumed that the fuel not accounted for was sold to users for use in motor vehicles and the department shall assess the tax and penalty due against the seller.

(3) The department shall give to the user or seller written notice of the assessment. The notice may be served personally or by mail. If made by mail, service shall be made by depositing the notice in the United States mail, postage prepaid, addressed to the user or seller at the address as it appears in the records of the department.