George P. Mitchell, an oil tycoon, philanthropist and champion of the controversial extraction method known as hydraulic fracturing, died Friday morning at his home in Galveston, Texas. He was 94, the Houston Chronicle reported.

Mitchell studied petroleum engineering and geology at Texas A&M University, graduating in 1936. He later became an Amoco engineer, eventually creating his own energy company called Mitchell Energy & Development Corp.

Mitchell is credited with starting the development of the U.S. shale oil and gas boom by being the first to break shale rock deposits trapping oil and gas deep inside the earth by hydraulic fracturing, or fracking. The technique, which he demonstrated as commercially viable in the 1990s, enabled him to turn the Barnett Shale of Texas into a highly profitable area.

Fracking is a drilling technique that blasts millions of gallons of water and chemicals to extract natural gas or oil from fractured rocks. The drilling technique has been heavily criticized, and some environmentalists contend fracking contaminates groundwater.