El Petróleo

http://www.clarin.com/diario/2006/04/27/elpais/p-02001.htm

http://www.alfinal.com/petroleo/petroleo.shtml

http://www.eco2site.com/informes/petroleo.asp

http://canarias24horas.com/index.php/2007102539291/ciencia/la-energia-eolica-produce-agua-mas-barata-que-el-petroleo.html

http://angeles.conectate.gob.pa/servlet/SBReadResourceServlet?rid=1221161007468_2113046591_100&partName=htmltext