An animated map from the U.S. Energy Information Administration shows the shift in Pennsylvania from vertical to horizontal wells.
It looks at the drilling from January 2005 through April 2012 in the Marcellus shale.
The horizontal wells first appeared in Pennsylvania in 2008.
More than 2,000 wells a year have been drilled in Pennsylvania from 2005-2012.
You can access the map at Marcellus Drilling News by clicking here.
The Marcellus Drilling News also reports that natural gas production is up significantly in Pennsylvania.
That's because horizontal wells are far more prodctive than vertical wells.
Chesapeake Energy Corp,the Oklahoma-based firm is the No. 1 driller in Ohio.
Rig Count Interactive Map by Baker Hughes, an energy services company.
Shale Sheet Fracking, a Youngstown Vindicator blog.
The Ohio Environmental Council, a statewide eco-group based in Columbus.
Earthjustice, a national eco-group.
People's Oil and Gas Collaborative-Ohio, a grass-roots group in Northeast Ohio.
Concerned Citizens of Medina County, a grass-roots group.
No Frack Ohio, a Columbus-based grass-roots group.
Fracking: Gas Drilling's Environmental Threat by ProPublica, an online journalism site.
Pipeline, blog from Pittsburgh Post-Gazette on Marcellus shale drilling.
Allegheny Front, environmental public radio for Western Pennsylvania.