Year	constant 2011 PPP $ per kg of oil equivalent
1990	8.61195009419733
1991	8.81885462522109
1992	8.69003237111921
1993	8.58929939229947
1994	8.22665460523001
1995	8.23812834546373
1996	8.31884109232957
1997	8.32048638119238
1998	8.38169001396838
1999	8.22965122504554
2000	8.29413666533837
2001	8.46441489539493
2002	8.48922192423734
2003	8.68493074505978
2004	8.60138573827835
2005	8.77635553554569
2006	8.91529956247789
2007	9.14537826078062
2008	9.40235457670686
2009	9.32922848061791
2010	9.1824578980295
2011	9.90765928509825
2012	10.2809904749599
2013	10.4126855862975
2014	10.7576679878741
2015	11.0349779869253