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.
On Tuesday, activists in California called for a ban on fracking.
The announcement came from Environment California, Citizens Coalition for a Safe Community, Grasroots Coalition, filmmaker Josh Fox and the national consumer group Food & Water Watch.
"Environment California supports a ban on fracking until it can be done safely and without endangering our lives, our health and the environment," said spokesman Dan Jacobson. "We need to move away from the production and use of fossil fuels and toward a clean renewable energy future."
To date, 50,000 Californians have signed petitions against fracking.