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.
Natural gas totals from the Marcellus shale in Pennsylvania grew by 42 percent from the second half of 2011 and are up 107 percent from the first six months of 2011.
The production numbers were released ny the state after Chsapeake Energy's totals were added into the state numbers.
The state's Marcellus shale produced 895 billion cubic feet of natural gas in the first six months of 2012.
That compares to 630 billion in the second half of 2011 and 432.5 billion cubic feet in the first half of 2011.
Bradford County remains No. 1 for natural gas volume with 235 billion cubic feet per day or roughly 25 percent of the state total.
The two biggest wells are both owned by Citrus Energy in Meshoppen. One produces 4.5 billion cubic feet per day; the other 2.9 billion cubic feet per day.