1 barrel of oil is 35 UK gallons, which would weigh 350 lbs. if it was water. The lightest naturally produced crude oils have a density about 0.85 that of water, so a barrel would weigh just under 300 lbs. The density of the very heaviest oils can reach 1.05, or nearly 370 lbs. per barrel. See also US liquid barrels, US federal barrels, US dry barrels and UK barrels. US Barrels (Oil) to Liters formula. L = US bbl oil _____ 0.0062898. Liters. Basic unit of volume in the metric system. A liter of water weighs one kilogram. US Barrels (Oil) to Liters table. Start Crude Oil Measurement. Crude oil, as shown in Figure 15, is measured in units of volume, weight and thermal energy. The standard volume unit for crude oil measurement, the 42-gallon barrel ("bbl"), dates back to the 1860s, when Pennsylvania producers actually stored and transported petroleum in wooden barrels. To this day you may hear a