Year	constant 2011 PPP $ per kg of oil equivalent
1990	4.72997246288554
1991	4.68363547083055
1992	4.7415582254777
1993	4.78046905661562
1994	4.87569434732194
1995	4.94330293044836
1996	5.01082593835962
1997	5.1807081899981
1998	5.37215457163707
1999	5.4803587145224
2000	5.5539611733852
2001	5.71787498460477
2002	5.76305151861795
2003	5.87946839253251
2004	5.97462072831274
2005	6.15319596892325
2006	6.38971922176047
2007	6.40593916708359
2008	6.54785033296416
2009	6.70164365358698
2010	6.72929411534917
2011	6.8925231284881
2012	7.15122849359155
2013	7.20032398167103
2014	7.25578761691717
2015	7.57675810490817