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.
Last week, New York's Cornell University reported that a new study has found dozens of cases of illness, death and reproductive issues in cows, horses, goats, llamas, chickens, dogs, cats, fish and other wildlife and humans.
It said those conditions could be the result of exposure to gas-drilling operations.
The authors of the study interviewed animal owners in Ohio and five other states and cited 24 cases where animals were potentially affected by gas drilling and hydraulic fracturing or fracking.
Making a direct link between fracking and illness is not possible due to incomplete testing, proprietary secrecy on some chemicals used in fracking and non-disclosure agreements that seal testimony and evidence when lawsuits are settled.
"We have a number of case studies -- they don't tell us about the prevalence of problems associated with hydraulic fracturing, but they do tell us things can happen," said Robert Oswald, a professor of molecular medicine at Cornell U's College of Veterinary Medicine.
He was one of the two authors, along with veterinarian Michelle Bamberger.
You can read more about the study here.