The most extensively developed to date has been the Barnett shale near Dallas Fort Worth TX, the Marcellus covering New York, Pennsylvania and West Virginia, and the Eagle Ford in Texas/New Mexico.
Horizontal drilling
This new technique, in which a drill can go into the earth for several miles and then turn so as to drill horizontally, has made the vast gas shale fields productive. Since the shale formations are hard rock will trillions of micro pores filled with natural gas it is necessary to crack this rock to let the gas out. This process is called fracing. IER will discuss fracing further elsewhere.