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.
Ohio's 177 injection wells handled about 12 million 42-gallon barrels of briny waste in 2011, and 53 percent of that brine came from Pennsylvania and other states.
In 2010, Ohio had handled about 8.5 million barrels of brine.
Ohio made an estimated $1.5 million in fees imposed on the brine injection wells, the Youngstown Vindicator reported last week.
In 2010, Ohio imposed a fee of 5 cents per barrel on brine that originates in Ohio and a fee of 20 cents a barrel for brine from outside of Ohio.
One injection well near Youngstown closed on Dec. 30 following a dozen earthquakes that Ohio now says is tied to injecting the briny waste under pressure near an unknown fault line 9,000 feet below ground. No problems have been reported at the other 176 injection wells.
Stark and Portage counties are tied for the most injection wells with 16 each.