Del. Code tit. 30, § 5210

Every motor carrier shall keep such records, in such form as the Department of Transportation reasonably may prescribe, as will enable the carrier to report and enable the Department of Transportation to determine the total number of over-the-road miles traveled by its entire fleet of motor vehicles, the total number of over-the-road miles traveled in Delaware by the entire fleet, the total number of gallons of motor fuel used by the entire fleet and the total number of gallons of motor fuel purchased in Delaware for the entire fleet. All such records shall be safely preserved for a period of 3 years in such manner as to insure their security and availability for inspection by the Department of Transportation or any authorized employee engaged in the administration of this chapter. Upon application in writing stating the reasons therefor, the Department of Transportation may, at its discretion, consent to the destruction of any such records at any time within the period if such records pertain to a period which has been audited by the Department of Transportation.