Year	constant 2011 PPP $ per kg of oil equivalent
1990	5.07866270668131
1991	4.7098826672651
1992	4.83220840930863
1993	4.57281914508814
1994	4.45094880986155
1995	4.87405182009705
1996	4.69710678302111
1997	4.81205239726966
1998	5.0258957653076
1999	5.26655924019359
2000	5.57108091828982
2001	5.56983945022722
2002	5.38274533292411
2003	5.20733434408704
2004	5.35235198545437
2005	5.96093139228009
2006	5.70119474328381
2007	6.08858631874857
2008	6.38379584884787
2009	6.20069174511442
2010	5.8353194270536
2011	6.22297104084156
2012	6.35984671668273
2013	6.44650863393948
2014	6.27962185272182
2015	6.59677856011724