A tanker is a merchant ship designed for the transport of liquids in bulk. Petroleum tankers fall into two main categories: the crude tanker and the product tanker.


Tankers vary in size of capacity from small tankers of several hundred tons, to very large tankers of several hundred thousand tons. Tankers carry a wide range of products such as:
  • hydrocarbon products such as oil, liquefied petroleum gas (LPG), and liquefied natural gas (LNG)
  • chemicals, such as ammonia, chlorine, and styrene monomer
  • fresh water
  • wine

Tankers date to the end of the 19th century and are a relatively new concept. The technology for transporting bulk liquids simply wasn't available before. The ships were loaded with liquids transported in casks. This had to be done because carrying bulk liquids posed many problems on older ships:

  • The holds of timber ships were not water or air-tight enough to prevent leaking of liquid cargo. This was solved by the development of iron and steel hulls.
  • Bulk liquids need to be loaded and unloaded utilising pumps. With the development of steam engines, early pumps and piping systems helped in transport of bulk liquids. Before the useage of pumps, the liquids were transported in casks and loaded and unloaded using cranes.
  • Free Surface Effect that poses dangers to stability of the ships. While the liquids were transported in casks there was no risk of destabilizing the ship. This problem was later solved using extensive sub-division of the transport tanks.

The beginnings of oil industry marked the birth of the first Oil Tankers. They were much sought because it was much cheaper to transport the refinery products in bulk. Today, large storage tanks ashore are used for storing the products before they are divided into smaller volumes and transported to customers.

Tanker capacity

Tankers used for liquid fuels are classified according to their capacity.

In 1954 Shell Oil developed the average freight rate assessment (AFRA) system which classifies tankers of different sizes. To make it an independent instrument, Shell consulted the London Tanker Brokers’ Panel (LTBP). At first, the groups were divided as General Purpose tankers (under 25,000 DWT), Medium Range (25,000 - 45,000 DWT) and Large Range (larger than 45,000 DWT). As the ship became larger in the second half of the 20th century, this system was rescaled:

  • 10,000–24,999 DWT: General Purpose tanker
  • 25,000–44,999 DWT: Medium Range tanker
  • 45,000–79,999 DWT: Large Range 1 (LR1)
  • 80,000–159,999 DWT: Large Range 2 (LR2)
  • 160,000–319,999 DWT: Very Large Crude Carrier (VLCC)
  • 320,000–549,999 DWT: Ultra Large Crude Carrier (ULCC)


Petroleum Tankers
Class Length Beam Draft Typical Min DWT Typical Max DWT
Seawaymax 226 m 24 m 7.92 m 10,000 mt 60,000 mt
Panamax 294.1 m 32.3 m 12 m 60,000 mt 80,000 mt
Aframax       80,000 mt 120,000 mt
Suezmax     16 m 120,000 mt 200,000 mt
VLCC (Malaccamax) 470 m 60 m 20 m 200,000 mt 315,000 mt
ULCC       320,000 mt 550,000 mt


The most popular size range among the larger VLCCs is between 279,000 and 320,000 DWT. There are about 380 vessels in this range. Only seven vessels are larger than this range, and there are about 90 in the range between 220,000 and 279,000 DWT.


Image:Distribution of supertanker sizes.png