Year	constant 2011 PPP $ per kg of oil equivalent
1990	6.38730323658446
1991	6.38818090542547
1992	6.43667072979294
1993	6.4138920554358
1994	6.49592865018646
1995	6.54065716618776
1996	6.54192099607924
1997	6.71395922026281
1998	6.86242576740729
1999	6.96150548415591
2000	7.08897092928123
2001	7.18131794285795
2002	7.23379660269674
2003	7.31211441383087
2004	7.40870992221645
2005	7.60056356703363
2006	7.81833077110447
2007	7.98026654479241
2008	8.0851330841774
2009	8.15941015178358
2010	8.09720388875227
2011	8.43723278029533
2012	8.5792250697096
2013	8.67916530375194
2014	8.87999192426294
2015	9.15359340031337