Tanker vessels may be classified by size:
• Ultra Large Crude oil Carriers (ULCC) 500,000 DWT
• Very Large Crude oil Carriers (VLCC) 200,000-300,000 DWT
• Suezmax 120,000-200,000 DWT
• Aframax 70,000-120,000 DWT
• Panamax 50,000-70,000 DWT
• Handymax 30,000-50,000 DWT
• Handysize up to 30,000 DWT
The main tanker cargoes include crude oil, oil products (gasoline, diesel oil, biofuels), chemicals (petrochemicals, acids), vegetable oils, and molasses. Typical modern tankers are of a double hull/double bottom design.
Cargo is carried in a series of tanks separated by a center bulkhead between the port and starboard sides of the ships. There might be up to twelve cargo tanks on a typical Suezmax vessel. Loading and discharging is carried out by a series of cargo pumps that serve each tank and are connected via a central manifold on deck to cargo lines and shore hoses. The ships are equipped with a small cargo crane on deck for handling cargo hoses and slop tanks for holding oil residue removed during the tank-cleaning procedures. Modern ships are equipped with crude oil washing (COW) and inert gas systems (IGS). Important ship specifications include the deadweight/GT/NT of the ship, the draft of
the ship, the speed and consumption of the ship (main and auxiliary engines) when laden and in ballast, as well as the tank sizes and cargo pump specifications.