Year	constant 2011 PPP $ per kg of oil equivalent
1990	4.40723224963662
1991	4.25579769247926
1992	4.25848107320566
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	4.59759992967126
2005	4.77716790175088
2006	4.98789103755358
2007	5.11141442161631
2008	5.07073494337046
2009	5.21904606303887
2010	5.3642452811842
2011	5.4529695602564
2012	5.55767933796446
2013	5.73243885370002
2014	5.88656327279607