75 Pa. C.S. § 9610
Every motor carrier shall keep such records, in such form as the department reasonably may prescribe, as will enable the carrier to report and enable the department to determine the total number of miles traveled by its entire fleet of qualified motor vehicles, the total number of miles traveled in this Commonwealth 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 this Commonwealth for the entire fleet. All such records shall be safely preserved for a period of four years in such manner as to insure their security and availability for inspection by the secretary or any authorized employee engaged in the administration of this chapter. Upon application in writing, stating the reasons therefor, the department may, in its discretion, consent to the destruction of any such records at any time within that period if the records pertain to a period which has been audited by the department. Every taxpayer shall retain records required by this chapter at a place within this Commonwealth, but a taxpayer who elects to retain records outside of this Commonwealth shall assume reasonable out-of-state audit expenses.
75 Pa.C.S. § 9610