Year	constant 2011 PPP $ per kg of oil equivalent
2005	6.73620029674967
2006	6.66449584526844
2007	7.05535384839826
2008	7.0403402241939
2009	8.31317708253872
2010	7.39327549429446
2011	7.97147863213231
2012	8.21734092157373
2013	9.20732776091384
2014	9.61903675708654