"Supertankers" are the largest tankers, including very large crude carriers (VLCC) and ULCCs with capacities over 250,000 DWT. These ships can transport 2,000,000 barrels (320,000 m3) of oil/318 000 metric tons.[46] By way of comparison, the United Kingdom consumed about 1.6 million barrels (250,000 m3) of oil per day in 2009.[47] ULCCs, commissioned in the 1970s, were the largest vessels ever built, but the longest ones have already been scrapped; only a few ULCCs remain in service, none of which are more than 400m long.[48]
Because of their great size, supertankers often can not enter port fully loaded.[28] These ships can take on their cargo at off-shore platforms and single-point moorings.[28] On the other end of the journey, they often pump their cargo off to smaller tankers at designated lightering points off-coast.[28] A supertanker's routes are generally long, requiring it to stay at sea for extended periods, up to and beyond seventy days at a time.[28]