Year	constant 2011 PPP $ per kg of oil equivalent
1990	5.61712925059909
1991	5.38231422431678
1992	5.56579748596322
1993	5.45502615259058
1994	5.31299211218846
1995	5.45726528179572
1996	5.41461936069037
1997	5.71943250519416
1998	5.8577957853745
1999	6.23273726690532
2000	6.88448747635243
2001	6.58101099588315
2002	6.5551667017145
2003	6.86437400971028
2004	6.89200415218543
2005	7.22618345474135
2006	7.77105748282119
2007	8.05953583853388
2008	8.08869679235046
2009	8.3768421276398
2010	7.91993346288083
2011	8.30549026055805
2012	8.22771097225251
2013	8.45663405361218
2014	8.90253668231414
2015	8.95559775370564