Oregon Revised Statutes Revenue and Taxation § 319.310

(1) The Department of Transportation may require any person who makes claim for refund of tax upon motor vehicle fuel to furnish a statement, under oath, giving the occupation, description of the machines or equipment in which the motor vehicle fuel was used, the place where used and such other information as the department may require.

(2) The department may investigate claims and gather and compile such information in regard to the claims as it considers necessary to safeguard the state and prevent fraudulent practices in connection with tax refunds and tax evasions. The department may, in order to establish the validity of any claim, examine the books and records of the claimant for such purposes. The records shall be sufficient to substantiate the accuracy of the claim and shall be in such form and contain such information as the department may require. Failure of the claimant to maintain such records or to accede to the demand for such examination constitutes a waiver of all rights to the refund claimed on account of the transaction questioned.