Barrel (unit) continued to use the same size barrels. In the worldwide oil industry, an oil barrel is defined as 42 US gallons, which is about litres or 35 imperial gallons. Oil companies that are listed on American stock exchanges typically report their production in terms of volume and use the units of bbl, Mbbl (one thousand barrels), or MMbbl (one million barrels) and occasionally for widest comprehensive statistics the Gbbl (or sometimes Gbl) denoting a billion. There is a conflict concerning the units for oil barrels (see ). For all other physical quantities, according to the International System of Units, the
History of the oil shale industry in the United States process, and production was limited by the small supply of petroleum that seeped into his salt wells. On 28 August 1859, Edwin Drake discovered oil in a well 70 feet deep along Oil Creek, south of Titusville, Pennsylvania. The well made only 12 to 20 barrels per day, but the discovery set off a boom in oil drilling up and down Oil Creek, and then all down the Ohio valley, to Ohio, Kentucky, and Virginia, the same area where many shale oil retorts were located. In 1861, petroleum flooding onto the market drove the price down to US$0.52 per barrel,