Year	constant 2011 PPP $ per kg of oil equivalent
1990	4.40422290894798
1991	4.25579769247926
1992	4.25848107320567
1993	4.07619478255709
1994	4.05459949115255
1995	4.02817745168701
1996	4.11150624790121
1997	4.14408638056141
1998	4.19121513598648
1999	4.13957074015002
2000	4.25489043163086
2001	4.28024347398686
2002	4.49261478435457
2003	4.48231198989238
2004	4.59716116201567
2005	4.77623020048038
2006	4.98693095352221
2007	5.10973165211344
2008	5.07073494337046
2009	5.21904606303887
2010	5.3642452811842
2011	5.4529695602564
2012	5.55767933796446
2013	5.73243885370001
2014	5.88656327279607