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.
California Gov. Jerry Brown says he will consider opening the fourtgh-largest oil-producing state to a drilling method known as hydraulic fracturing or fracking to increase natural-gas production.
Brown said the technique has been long been used in the oil-rich San Joaquin Valley and said he would likely permit more widespread fracking, if environmental consequences can be minimized.
"I'm an optimist," Brown said Friday at a conference in Santa Barbara. "I'm going to look at it."