Year	constant 2011 PPP $ per kg of oil equivalent
1990	6.37186517932756
1991	6.21131368937013
1992	6.23765869722749
1993	6.32730229581183
1994	6.15491941059708
1995	6.1912398409236
1996	5.97282916807856
1997	6.1940318035251
1998	6.21325352084846
1999	6.40899351165153
2000	6.55958545863866
2001	6.63121919871124
2002	7.02259847400396
2003	6.79614877583379
2004	7.00904774732647
2005	7.16445648528999
2006	7.40925488317067
2007	7.79908652763849
2008	7.63004027215004
2009	7.76579006062589
2010	7.41693718269195
2011	8.10714610472616
2012	8.48732648881338
2013	8.20696213135881
2014	8.78137079001799
2015	8.92123008017171