This is a list of container ships with a capacity larger than 20,000 twenty-foot equivalent units (TEU). Container ships have been built in increasingly larger sizes to take advantage of economies of scale and reduce expense as part of intermodal freight transport. Container ships are also subject to certain limitations in size. Primarily, these are the availability of sufficiently large main engines and the availability of a sufficient number of ports and terminals prepared and equipped to handle ultra-large container ships. Furthermore, some of the world's main waterways such as the Suez Canal and Singapore Strait restrict the maximum dimensions of a ship that can pass through them.