Year	constant 2011 PPP $ per kg of oil equivalent
1990	3.40883637141788
1991	3.28745730346351
1992	3.21867412772703
1993	3.22998384328079
1994	3.24712908969065
1995	3.26229025344737
1996	3.30006592984745
1997	3.50978811735464
1998	3.50801322877091
1999	3.57401451429237
2000	3.80308341774198
2001	3.91477901856188
2002	4.07563065966962
2003	4.18191657117893
2004	4.47435662066412
2005	4.77531747461523
2006	5.00068631211437
2007	5.32260269986732
2008	5.48875343980587
2009	5.57624517991083
2010	5.46996709427071
2011	5.52246345052356
2012	5.64793260717705
2013	5.96961160077137
2014	6.30574667861088