1. Ultralarge crude carriers (ULCCs). The very largest ships, these have a length in the neighbourhood of 415 metres (1,350 feet) and a capacity of 320,000 to more than 550,000 dwt. They carry from two million to well more than three million barrels of crude.

2. Very large crude carriers (VLCCs). These ships, with a length of some 330 metres (1,100 feet), have capacities between 200,000 and 320,000 dwt. They carry in the area of two million barrels.

3. Suezmax. The largest ships that can transit the Suez Canal, these tankers are some 275 metres (900 feet) long and have a capacity of 120,000 to 200,000 dwt. They carry about 800,000 to more than 1,000,000 barrels.

4. Aframax. The maximum size of vessel to use the Average Freight Rate Assessment method for calculating shipping rates, these tankers are around 240 metres (790 feet) long and have capacities of 80,000 to 120,000 dwt. They carry roughly 500,000 to 800,000 barrels.

5. Panamax. The maximum size that can transit the Panama Canal, these tankers range in length between 200 and 250 metres (650 and 820 feet) and have capacities of 50,000 to 80,000 dwt. They carry 350,000 to 500,000 barrels.

6. Handymax, Handysize, Coastal, and other classes. These ships have capacities of less than 50,000 dwt and lengths up to approximately 200 metres (650 feet).