Year	constant 2011 PPP $ per kg of oil equivalent
1990	4.10939366721825
1991	4.03359565398709
1992	3.97739687874465
1993	3.95083864534301
1994	3.98763715290505
1995	4.0413248858451
1996	4.02692553234713
1997	4.15629652583844
1998	4.34073730315995
1999	4.43894373887293
2000	4.53736698153382
2001	4.68700993260835
2002	4.81351448792635
2003	4.65394099846241
2004	4.68886871880199
2005	4.81263530755515
2006	4.99782905390293
2007	5.06845808419082
2008	5.07582596299922
2009	5.11974906616372
2010	5.22530192411118
2011	5.25427071922064
2012	5.4109599914425
2013	5.47155143862742
2014	5.46345470555212
2015	5.65093446611668