1. BP Statistical Review of World Energy, June 2015. Available at
https://www.bp.com/content/dam/bp/pdf/energy-economics/statistical-review-2015/bp-statistical-review-of-world-energy-2015-full-report.pdf
2. EIA Table 9-2 Technically recoverable U.S. dry natural gas reserves as of Jan 1, 2013. Available at
http://www.eia.gov/forecasts/aeo/assumptions/pdf/oilgas.pdf
3. U.S. Coal reserves, The U.S. Energy Information Administration, Mar 24 2015. Available at
http://www.eia.gov/coal/reserves/