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.
Youngstown recorded its 12th earthquake since last March last weekend.
The quake on Jan. 13 was a 2.1-magnitude.
The quakes have been centered at a now-closed injection well for drilling wastes west of downtown Youngstown in Youngstown Township.
The Ohio Department of Natural Resources continues to investigate the links between the quakes and the injection well operated by the D&L Energy Group.
The biggest quake, a 4.0, rattled Northeast Ohio on Dec. 31.
According to the Youngstown Vindicator, Ohio is looking at a ban on injection wells deeper than 8,000 feet, but such a rule has not yet been finalized.
Such a ban might produce fewer quakes if the injection wells wqere shallower, officials said.