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 west of the Mississippi River. These include some, such as the Woodford Shale of Oklahoma, which are near-stratigraphic equivalents to the Devonian/Mississippian shales of the eastern US. The largest oil-shale resource in the world is contained in the Eocene Green River Formation in Colorado, Utah, and Wyoming in three basins: the Piceance Basin, Green River Basin, and Uinta Basin. The Green River oil shales have been the focus of most efforts of the past hundred years to establish an American oil shale industry. The Green River oil “shale” is actually a marl, and some beds yield up to 70 gallons