Year	constant 2011 PPP $ per kg of oil equivalent
1990	4.48491887135231
1991	4.55186674080088
1992	4.62823271053787
1993	4.73190045213729
1994	4.8671702913003
1995	4.88480404604734
1996	5.01929094951989
1997	5.25179122364706
1998	5.39896221787727
1999	5.49501440090839
2000	5.70117245649647
2001	5.74389112174208
2002	5.79946310746371
2003	5.67406413426285
2004	5.67501338009336
2005	5.73369080225491
2006	5.84587024949895
2007	6.06174862808771
2008	6.20913963479327
2009	6.20254407850649
2010	6.1954793589522
2011	6.25189080457661
2012	6.35873230389762
2013	6.5268806561686
2014	6.70889385730028