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.
Spears & Associates reported that hydraulic fracturing or fracking is expected to grow 19 percent worldwide in 2012 to a record $37 billion, Bloomberg News said.
North American spending on the technique is expected to top $30 billion in 2012, according to the Oklahoma-based company. It advises about 400 oil producers, hedge funds, equipment suppliers and manufacturers on energy-industry trends.
North America accounted for 87 percent of the fracking market in 2011.
The eastern United States including Ohio, Pennsylvania and West Virginia with the Utica and Marcellus shales accounted for $2 billion in fracking in 2011, Spears said..
In the United States, 19,000 new horizontal wells are expected in 2012, up from 2011's record-high 16,000, said Spears.
More than half of the fracking services in the United States were provided by four companies: Halliburton Co., Schlumberger Ltd., Baker Hughes Inc.'s BJ Services and Frac Tech Services LLC.
Halliburton is No. 1 with 18 percent, followed by Schlumberger with 13 percent, Spears said.
Those companies do the fracking for energy companies like Oklahoma-based Chesapeake Energy Corp., the biggest player in Ohio's Utica shale.