The Leader-Enterprise has a good summary of development in Pennsylvania to date: "Across the state, 6,200 shale gas wells have been drilled, though only 3,550 are currently producing. Even with just that production, Pennsylvania rose to the third largest producer in the United States in 2012, behind only Texas and Louisiana. In 2010, the Commonwealth ranked 14th. *** In the U.S., 42 percent of the gas produced comes from shale and much of it comes from the Marcellus shale layer."
Read it all.