1. Key world energy statistics;International Energy Agency (IEA),2014
2. BP Energy Outlook 2035, February 2015. http://www.bp.com/content/dam/bp/pdf/energy-economics/energy-outlook-2015/Energy_Outlook_2035_booklet.pdf.
3. When will fossil fuel reserves be diminished?;Shafiee;Energy Policy,2009
4. CO2 emissions from fuel combustion HIGHLIGHTS;International Energy Agency (IEA),2014
5. World energy data, http://www.eia.gov (accessed September 2015).