A standard-size barrel filled with the most common oils (petroleum oil, crude oil or diesel fuel oils) weighs between 125 and 140 pounds. However, the weight of a barrel of oil varies based on the type of oil in the barrel and the size of the barrel.
A standard-size barrel holds 42 U.S. gallons. If one fills a standard-size barrel with petroleum oil that has a density of 881 kg/m3, then that barrel weighs about 140 kilograms. If one fills the same barrel with crude oil with a density of 790 kg/m3, that barrel weighs about 125 kg. In order to get a metric tonne of oil, one would need about 7.33 barrels of oil.