Oil tankers are often classified by their size as well as their occupation. The size classes range from inland or coastal tankers of a few thousand metric tons of deadweight (DWT) to the mammoth ultra large crude carriers (ULCCs) of 550,000 DWT. Tankers move approximately 2,000,000,000 metric tons (2.2×109 short tons) of oil every year.[4][5] Second only to pipelines in terms of efficiency,[5] the average cost of oil transport by tanker amounts to only two or three United States cents per 1 US gallon (3.8 L)