1. BP: Statistical Review of World Energy, http://www.bp.com/en/global/corporate/energy-economics/statistical-review-of-world-energy.htm (2016)
2. Wikipedia: World Energy Sources, http://en.wikipedia.org/wiki/World_energy_resources (2015)
3. Encyclopaedia Britannica: Greek Fire, Online, www.britannica.com/technology/Greek-fire/ (2015)
4. SETatWork: Good practice: Use of waste heat from refining industry, Sweden, SETat Work Good Practice #20, http://www.setatwork.eu/database/products/R179.htm (2015)
5. G. Tverberg: Consumption of energy by source since 1820, Our Finite World, http://ourfiniteworld.com/2012/03/12/world-energy-consumption-since-1820-in-charts/ (2015)