Year	constant 2011 PPP $ per kg of oil equivalent
1990	8.31727913341911
1991	8.36694052402423
1992	8.48800550495395
1993	8.45683587104726
1994	8.65179265501336
1995	8.50710865102579
1996	8.37854767397866
1997	8.62077192491589
1998	8.72791213459393
1999	8.99225413317798
2000	9.21869774014461
2001	9.17774550676736
2002	9.27128490126299
2003	9.15072767707319
2004	9.23166404175962
2005	9.37046767841746
2006	9.6537207860088
2007	10.1219638820774
2008	10.1926197840487
2009	10.2998436354821
2010	10.1513248813332
2011	10.7441332326282
2012	10.7487334494911
2013	10.8100991072212
2014	11.3882831735856
2015	11.4472131404048