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.
It took more than 10 months for the Carnegie Museum of Natural History to determine how many Marcellus shale natural gas wells exist in Pennsylvania.
The answer: 9,848, according to the museum's Powdermill Nature Reserve.
Of that total, 6,391 are either drilled and/or producing.
There are an additional 2,457 active permits that could eventually be drilled.
Another 349 wells have either been abandoned, plugged, declared inactive, shut down or their status is unknown.
The total is since 2000.
The list is believed to the first comprehensive list of wells in Pennsylvania.
The state's records kept by the Department of Environmental Protection are incomplete and contain errors because of the rush to drill in the last four years, officials said.
The state said it may study the database to correct errors in its records.
The public may be able to access the Powdermill's new database by late June or early July.
Right now, it is only open researchers and government officials.
The research project got under way after a museum intern inquired as to how many Marcellus wells existed in Pennsylvania.