R.I. Gen. Laws § 31-36.1-5

There is levied and imposed upon motor carriers a tax at the rate specified in § 31-36-7 on the use of fuel for the propulsion of qualified motor vehicles on the public highways within this state. The tax, with respect to fuel purchased instate, shall be paid at the time of purchase as provided in chapter 36 of this title. The tax, with respect to fuel purchased outside this state shall be paid when the quarterly returns required in § 31-36.1-11 are filed with the administrator.