King, G. E.: "Hydraulic Fracturing 101: What Every Representative, Environmentalist, Regulator, Reporter, Investor, University Researcher, Neighbor and Engineer Should Know About Estimating Frac Risk and Improving Frac Performance in Unconventinal Gas and Oil Wells," SPE Paper 152596, to be presented at the SPE Hydraulic Fracturing Technology Conference, The Woodlands, TX. 6-8 February 2012.

Available at the Kansas Geological Service website.

Broomfield, M.:"Support to the identification of potential risks for the environment and human health arising from hydrocarbons operations involving hydraulic fracturing in Europe" Report prepared for the European Commission, September 2012

Available at the European Commission website.

U.S. EPA, U. S. Environmental Protection Agency: Plan to Study the Potential Impacts of  Hydraulic Fracturing on Drinking Water Resources. November 2011

Available at the U.S. EPA website.