1. AMSO, Oil shale extraction methods, [Online]. Available from: http://amso.net/about-oil-shale/oil-shale-extraction-methods/.
2. HowStuffWorks, What's oil shale? [Online]. Available from: http://s.hswstatic.com/gif/oil-shale-2a.jpg.
3. Council on Foreign Relations, The shale gas and tight oil boom: U.S. States' economic gains and vulnerabilities, [Online]. Available from: http://www.cfr.org/united-states/shale-gas-tight-oil-boom-us-states-economic-gains-vulnerabilities/p31568.
4. yCharts, Us crude oil field production, [Online]. Available from: https://media.ycharts.com/charts/7f20a289fbe422ef0287d59f3c9c0c96.png.
5. Non-synfuel uses of oil shale;Knutson,1987