Year	constant 2011 PPP $ per kg of oil equivalent
1990	4.61570435309162
1991	4.53531498201364
1992	4.58704986927851
1993	4.53894698759392
1994	4.56230386054734
1995	4.60189997087605
1996	4.66978342850275
1997	4.69957410470349
1998	4.69574961853289
1999	4.67684710859502
2000	4.81685286267568
2001	4.87768262641057
2002	5.00753778091379
2003	5.11444045121258
2004	5.34092797612851
2005	5.56955014884282
2006	5.76829281685247
2007	5.96067873089126
2008	6.08371396209122
2009	6.3572959174311
2010	6.48937638797134
2011	6.50625707064037
2012	6.6019280571226
2013	6.86870893516646
2014	7.369358080654