1. Three main sources of unconventional gas; Total website;http://www.total.com/en/our-energies/natural-gas-/exploration-and-production/our-skills-and-expertise/unconventional-gas/presentation/specific-fields-201900.html.
2. Availability, economics, and production potential of North American unconventional natural gas supplies; INGAA Foundation, Inc. 2008; http://www.ingaa.org/File.aspx?id=7878.
3. Modern Shale Gas Development in the United States: A Primer; National Energy Technology Laboratory, 2009; http://www.netl.doe.gov/technologies/oil-gas/publications/epreports/shale_gas_primer_2009.pdf.
4. Annual Energy Outlook 2011; U.S. Energy Information Administration (EIA), 2011; http://www.eia.doe.gov/forecasts/aeo/.
5. World Shale Gas Resources: An initial assessment of 14 regions outside the United States; U.S. Energy Information Administration (EIA), April 2011; http://www.eia.gov/analysis/studies/worldshalegas/.