1. Statistical review of world energy;British Petroleum,2011
2. British petroleum energy outlook 2030,2011
3. U.S.D.O.E. HTTP://www.energy.gov/ (accessed 17.8.2011).
4. U.S.D.O.E. Energy Information Administration http://www.eia.doe.gov/ accessed 17.8.2011.
5. International Energy Agency http://www.iea.org/ accessed 17.8.2011.