1. IEA (2012) Statistics Database
2. Nitsch F (2007) Technologische und energiewirtschaftliche Perspektiven erneuerbarer Energien. Deutsches Zentrum für Luft- und Raumfahrt
3. PennWell Corporation, Oil & Gas Journal, Vol. 106.48 (December 22, 2008), except United States. Oil includes crude oil and condensate. Data for the United States are from the Energy Information Administration, U.S. Crude Oil, Natural Gas, and Natural Gas Liquids Reserves, 2007 Annual Report, DOE/EIA-0216(2007) (February 2009). Oil and Gas Journal’s oil reserve estimate for Canada includes 5.392 billion barrels of conventional crude oil and condensate reserves and 172.7 billion barrels of oil sands reserves
4. World Coal Institute
5. World Nuclear Association