Year	constant 2011 PPP $ per kg of oil equivalent
1990	7.35120676158484
1991	7.13190659775147
1992	7.36074155036835
1993	7.38834197969403
1994	7.55935680077869
1995	7.32065478287367
1996	7.18913427443053
1997	7.73843448387348
1998	8.0384177964099
1999	8.58603888665934
2000	8.86599900993412
2001	8.81728442638288
2002	8.71932853412396
2003	8.43708421689027
2004	8.46427078809803
2005	8.78423327093201
2006	9.19223327762157
2007	9.54975395668735
2008	9.84116411632652
2009	9.68315035503597
2010	9.17389262711838
2011	10.0500359943123
2012	9.88936980491179
2013	9.94604620033073
2014	10.6896211384095
2015	11.0879089737784