Miss. Code § 27-19-67
In the case of carriers of property in all classifications, the maximum gross weight of the vehicle, or combination of vehicles, and the provisions of Section 27-19-11 shall determine the amount of tax actually due. In the case of all carriers of property and all buses, the privilege license shall be construed to grant to the owner or operator the privilege of operating on the highways of this state, the designated vehicle, or combination of vehicles, with the total or combined gross weight specified by such license. No vehicle shall be operated on the highways of this state with a greater gross weight or in a higher tax classification than that for which such vehicle is licensed, except as may be otherwise provided in this article, but any vehicle may be operated in a lower tax classification than that in which such vehicle is registered, unless otherwise provided by this article, without payment of additional tax; provided that this shall not authorize any such vehicle to operate with a greater gross weight than that for which it is licensed regardless of the tax classification in which such vehicle is being operated. In the case of vehicles which are designed, constructed and used to carry no load other than the fixtures and equipment thereto attached and other tools, appliances and equipment used by the owner or operator thereof, the tax shall be based on the gross weight of the vehicle which is being or is to be operated on the highways.
In the case of vehicles which are rented or leased to others by the owner thereof, and vehicles commonly known as "U-Drive-It" vehicles, the tax shall be based on the type of the vehicle and the tax classification and gross weight bracket in which such vehicle is being or is to be operated.
Miss. Code § 27-19-67