The railway tank wagon or railway tanker 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, and 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, with all valving, and a protective cylindrical housing (dome) at the top. Loading and unloading are done through this opening.