Year	constant 2011 PPP $ per kg of oil equivalent
1990	4.54723184370468
1991	4.51143315060012
1992	4.51932488159539
1993	4.60715044294575
1994	4.57412790282844
1995	4.61713034564322
1996	4.71185298676855
1997	4.79561561980782
1998	4.83084549605826
1999	4.86823327257852
2000	5.0763617446191
2001	5.14953155805649
2002	5.16945136098578
2003	5.27719759343224
2004	5.44910016688285
2005	5.63989713918484
2006	5.83226767298755
2007	6.05396812739097
2008	6.22174989868466
2009	6.3207690184447
2010	6.48475333530676
2011	6.51179980152894
2012	6.64620205539862
2013	6.75664839033779
2014	6.74918085505407