Year	constant 2011 PPP $ per kg of oil equivalent
1990	6.06245077453123
1991	4.71931337383358
1992	4.52988459849189
1993	4.51546604906043
1994	4.35097563815962
1995	4.47844296152187
1996	4.72842600185181
1997	4.79663870046573
1998	6.01920499858264
1999	6.75627951088926
2000	6.71459753303964
2001	6.6035058948014
2002	6.46980542206663
2003	6.03186962994089
2004	6.76914483043683
2005	7.04642638024443
2006	7.50711563574157
2007	7.88924611396267
2008	7.98112258078795
2009	7.7926438376031
2010	7.888498473952
2011	7.39539043835147
2012	7.87598241644264
2013	7.69627666381328