35 ILCS 505/1.14
"Supplier" means any person other than a licensed distributor who (i) transports special fuel into this State; (ii) exports special fuel out of this State; or (iii) engages in the distribution of special fuel primarily by tank car or tank truck, or both, and who operates an Illinois bulk plant where he has active bulk storage capacity of not less than 30,000 gallons for special fuel as defined in Section 1.13 of this Law.
"Supplier" does not, however, include a person who receives or transports into this State and sells or uses special fuel under such circumstances as preclude the collection of the tax herein imposed, by reason of the provisions of the Constitution and laws of the United States. However, a person operating a motor vehicle into the State, may transport special fuel in the ordinary fuel tank attached to the motor vehicle for the operation of the motor vehicle without being considered a supplier. Any railroad licensed as a bulk user and registered under Section 18c-7201 of the Illinois Vehicle Code may deliver special fuel directly into the fuel supply tank of a locomotive owned, operated, or controlled by any other railroad registered under Section 18c-7201 of the Illinois Vehicle Code without being considered a supplier.
35 ILCS 505/1.14