A tanker is a ship-cistern used for industrial transporting of liquid materials. The tankers are the biggest trading vessels. Unlike other types of freighters they do not have a hold but loading containers (loading and unloading is made with the help of a network of pipes and pumps). Tankers are most frequently used for transportation of crude oil, however, they are also used for transporting chemicals and liquefied gas. Sizes of tankers differ - they have from several to a few hundreds thousand of displacement. Supertankers transporting crude oil belong to the largest ships of this kind. One of them, the TT Knock Nevis, is a vessel of the largest capacity - at one time it may take almost 650.000 m3 of crude oil.
