The Bradford oil field, in McKean County, is the largest in the state. There are currently 350,000 oil and gas wells drilled in Pennsylvania since 1859. The commercial development of natural gas came after the oil boom. During the early 1880s gas was used to fuel the engines at oil wells and to heat buildings. Pennsylvania now uses almost five times more gas than it produces.
Gas is piped in from western states.
In 1992, there were 365 oil and gas extraction establishments. Crude petroleum and natural gas accounted for 171 of the establishments while oil and gas field services accounted for 193. The earliest account of coal mining in Pennsylvania was recorded in 1752 at a place that is now downtown Pittsburgh. Pennsylvania's reserves of high quality coal are responsible for the emergence of the iron and steel, chemical, glass and metal- fabricating industries. It has been calculated that prior to mining, Pennsylvania had coal reserves of over 107 billion tons.