1. British Petroleum (BP). Statistical review of world energy 2006. See also: 〈http://www.bp.com/productlanding.do?categoryId=91&contentId=7017990〉.
2. Foss B. Oil prices settle at $ 77 a barrel. yahoo! News, July 14, 7:03 PM ET, 2006. Washington, US. See also: 〈http://news.yahoo.com/s/ap/20060714/ap_on_bi_ge/oil_prices;_ylt=Anc02jZWGvgM5noeu95Gc7OyBhIF;_ylu=X3oDMTA2Z2szazkxBHNlYwN0bQ--〉.
3. Energy Information Administration. Official energy statistics from the US government. See also: 〈http://www.eia.doe.gov/cneaf/coal/quarterly/html/t8p01p1.html〉.
4. Renewable energy: power for a sustainable future;Boyle,2004
5. Renewable energy perspectives and support mechanisms in Taiwan;Wu;Renew Energy,2006