Year	constant 2011 PPP $ per kg of oil equivalent
1990	7.41573092738749
1991	7.09370159640696
1992	7.14555365865682
1993	7.25251290586245
1994	7.47690287714316
1995	7.6475346358894
1996	7.51734969387634
1997	8.06758951572928
1998	8.25494987734609
1999	8.49870195446213
2000	8.75695715048628
2001	8.97306782967008
2002	9.40465392388311
2003	9.55499523493132
2004	9.82157472087361
2005	10.08366692226
2006	10.5145940228832
2007	11.1871874381003
2008	11.3231821168188
2009	11.500888298957
2010	11.3008727623013
2011	12.3884550294256
2012	12.1906245097933
2013	12.5851873725457
2014	13.8353415204618
2015	14.1136093879597