Tight oil is a light hydrocarbon contained in petroleum-bearing shale formations that have relatively low porosity and permeability. Tight oil is extracted at depths of 2 to 3 km on average, with the deepest wells taking up to six weeks to drill. Fracking technology is relatively new but is most developed in the United States, where tight oil could add up to 1 million barrels per day to total oil production by 2016, according to a report by the International Energy Association (IEA). Tight oil should not be confused with oil shale, which contains kerogen. Kerogen is a heavy mixture of organic chemical compounds, the soluble part of which is known as bitumen. Oil shale is a primitive form of oil that has not yet been converted into crude, because the sediment has experienced great heat or high pressure. It is typically found in shallow deposits and is mined, instead of drilled, with a consequent impact on the environment.