Abstract: A railway tank car of light weight and high cargo load capacity in which a tank shell structure is carried on and unified with an underframe including a stub sill at each end, a pair of spaced apart saddle bolsters, each joined to a respective one of the stub sills, and a center sill interconnecting the saddle bolsters. The tank shell rests on and is welded to the center sill, the saddle bolsters, and the stub sills, so that the tank shell is an integral part of the car, and both static and dynamic load forces resulting from train operation and from cargo loads are shared by the tank and the underframe. The underframe is constructed primarily of welded flat plate, with a minimum of specially formed parts and difficult welds, in order to simplify and minimize the costs of construction.