Tankers are designed to carry liquid cargoes (not just oil) although the carriage of crude oil has brought the tanker unwelcome attention and largely unjustified criticism. Oil tankers come in two basic flavours, the crude carrier, which carries crude oil, and the clean products tanker, which carries the refined products, such as petrol, gasolene, aviation fuel, kerosene and paraffin. Tankers range in all sizes, from the small bunkering tanker (used for refuelling larger vessels) of 1000 DWT tons to the real giants: the VLCC and the ULCC's
It should be remembered that over 60% of the world's oil is transported by these tankers, and over 99% of that arrives safely without causing pollution. Indeed most oil pollution seen on beaches comes from the engine rooms of vessels (of all types) and not from the cargo tanks of tankers.
To ensure that oil tankers transport to all parts of the world, and not just the affluent western countries where freight rates might be expected to be higher, (and therefore tankers congregate), there is a system called WORLDSCALE, which ensures that net freight earnings for tanker owners are the same, regardless of length of voyage and varying costs (such as bunkers and port dues), so that a tanker will earn (net) as much per day on a route that is long and arduous as they will on a short and low cost voyage. This ensures that tankers take their goods to all parts of the world and don't just concentrate on the lucrative Middle East to Western Europe or USA routes.