The Barnett Shale is a Mississippian-age rock formation beneath north-central Texas that became one of the most important U.S. shale-gas regions. Named for John W. Barnett after geologists identified the shale near a stream bearing his name, it was long known as both a source rock and cap rock for conventional oil and gas. Its low-permeability “tight” gas made extraction difficult until hydraulic fracturing and horizontal drilling made commercial production viable. Mitchell Energy’s work, especially the shift to slickwater fracturing in 1997, transformed the Barnett into the leading U.S. shale-gas play in the 2000s while also making it a major example of the economic benefits and environmental conflicts of urban shale development.