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.
Pennsylvania's Department of Environmental Protection has under-counted the number of wells producing Marcellus shale natural gas, according to the Pittsburgh Post-Gazette.
The problem has frustrated industry, elected officials and eco-groups.
A Sunday analysis by the newspaper showed there are 495 more wells producing gas or ready to produce gas than DEP has recorded as ever being drilled.
In addition, 182 of those wells don't show up on the state's Marcellus shale permit list.
DEP spokesman Kevin Sunday says the agency acknowledges problems and is working to clear up the data.
To see the story, go here.