Year	constant 2011 PPP $ per kg of oil equivalent
1990	3.08842834524028
1991	3.00883716453938
1992	1.92495863691597
1993	1.54978697559525
1994	2.25386098541219
1995	2.90797310330246
1996	3.21575844501431
1997	4.04955585187823
1998	4.51647524562966
1999	5.07498556727812
2000	5.01222213669377
2001	5.86364672859606
2002	6.2489624565831
2003	6.52610082160384
2004	6.71748702868405
2005	7.20609383020006
2006	7.38815688143159
2007	7.54629684329285
2008	8.59509310378053
2009	8.03797570112715
2010	8.46708488769863
2011	7.99744394188894
2012	8.13542396423818
2013	7.99691379111444
2014	7.42794063417498