Year	constant 2011 PPP $ per kg of oil equivalent
1990	6.23650353835643
1991	6.01812430927881
1992	5.95034830881701
1993	6.00747113618587
1994	6.09737453343393
1995	6.29482745068847
1996	6.29983392783531
1997	6.15478839538536
1998	6.29036119198659
1999	6.37658730044989
2000	6.34320244247575
2001	6.55817791522833
2002	6.85614964848706
2003	7.26297883093786
2004	7.37065165226043
2005	7.79568834698766
2006	8.01384834664028
2007	8.16422174014699
2008	7.95814632770476
2009	7.88045416010159
2010	7.62887274116769
2011	7.83680547195071
2012	7.63692039989878
2013	7.76919159124761
2014	7.58966658078849
2015	7.91450878133233