Year	constant 2011 PPP $ per kg of oil equivalent
1990	3.44984510116141
1991	3.35608160110683
1992	3.24889383737852
1993	3.46612803824739
1994	3.14532675212849
1995	3.18180166080225
1996	3.40868469139686
1997	3.39312498939967
1998	3.3469007691846
1999	3.49649519761019
2000	3.54356167326974
2001	3.61719178661244
2002	3.65569763672356
2003	3.78380174729607
2004	3.93641445901482
2005	4.08541131617631
2006	4.31159498884789
2007	4.67011660411765
2008	4.86428765455172
2009	5.18625379818016
2010	5.52294079153993
2011	5.51986766120219
2012	5.65795022021887
2013	5.62964641693006