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.
ProPublica's Abrahm Lustgarten reports on a new study that is raising concerns about fracking chemicals injected into the ground could migrate toward drinking water in the Marcellus shale area of Pennsylvania far more quickly that experts had predicted.
The study used computer modeling and concluded that "natural faults and fractures in the Marcellus, exacerbated by the effects of fracking itself, could allow the chemicals to reach the surface in a little as just a few years," he wrote.
The study was published in the journal Ground Water and was paid by two New York organizations that oppose hydraulic fracturing or fracking.
The industry disputed the findings.
You can read the ProPublica account here.