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.
The Marcellus Shale Coalition distributed a story from the Erie (Pa.) Times-News on how drilling for natural gas is likely to spread into the Erie area.
To date, no wells have been drilled in Erie or Crawford counties.
The area sits atop both the Marcellus and Utica shales.
It's just a matter of time, said Kathryn Klaber of the Marcellus Shale Coalition, a pro-drilling group, during a workshop at Penn State Behrend.
"There's no reason why the birthplace of the oil and gas industry won't play a major role," she said.
Elsewhere in northwest Pennsylvania, 74 wells have been drilled in Clarion County, 179 in Elk County and 211 in Potter County, according to state records.