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.
Production of Marcellus shale natural gas in Pennsylvania rose again in the second half of 2011, slightly exceeding projections.
The state reported that drillers produced the equivalent of 1.66 billion cubic feet of natural gas per day from July through December.
That's up from the 1.19 billion cubic feet per day int he previous six months, Pennsylvania reported.
That translates into a yearly average of about 1.42 billion cubic feet per day. That's up slightly from the previous industry projections of 1.3 billion for 2011