The tank wagon is a piece of railroad rolling stock designed to carry liquefied loads, petroleum products, liquid chemicals and gases .
Many variants exist in tank wagons due to the wide variety of liquids and gases that can be transported. Tank wagon can be insulated or non-insulated, pressurized or non-pressurized, railway carand designed for single or multiple loads. Non-pressurized cars have plumbing at the bottom for unloading, and may have an access port and a dome, housing various valving on the top. Pressurized cars have a pressure plate, railway car with all valving, and a protective cylindrical housing (dome) at the top. Loading and unloading are done through this opening.