Year	constant 2011 PPP $ per kg of oil equivalent
1990	5.57791525181472
1991	5.54773181550149
1992	5.69538390779189
1993	5.77207020031677
1994	6.04592947752111
1995	6.07956992851689
1996	6.0876604132176
1997	6.38472646726155
1998	6.52132058930442
1999	6.71042341393762
2000	6.9563802432072
2001	7.01446062165224
2002	7.15094494813482
2003	7.12692058366763
2004	7.3220320868503
2005	7.544080548865
2006	7.76946512009772
2007	8.15081213009264
2008	8.23842707305703
2009	8.37605600594474
2010	8.19305947269944
2011	8.47785855123737
2012	8.52191509622308
2013	8.73033607287958
2014	9.27586431071698