The substance produced from the treatment of kerogen, that hydrocarbon found in some shales, which is difficult and costly to extract. Shale is a dense rock formation common in many parts around the world which has long been known to contain natural gas. Production, however was impractical when the price of oil was low because the rock is not porous enough for the gas to flow. In the 1990s, however, companies figured out how to crack the shale using pressurized water, thus releasing the gas, with the technique being perfected in the Barnett Shale, a massive shale-gas field around Fort Worth, Texas which produces in 2008 about 4 bcf of natural gas per day. US shale plays could hold as much as 840 trillion cubic feet of gas, the equivalent of more than 140 billion barrels of oil, more than half the proven reserves of Saudi Arabia, but the amounts produced could eventually definitely be lower and production will require billions of dollars of drilling. Limited availability of drilling rigs, oil-field workers and pipelines as well as environmental and regulatory constraints will restrict how fast production will advance. The discovery however of this new source of natural gas has increased production and could change the supply and demand equilibrium