Year	constant 2011 PPP $ per kg of oil equivalent
1990	8.5071470261201
1991	8.67046139372909
1992	8.85814437485767
1993	8.5886530916218
1994	9.22402413364407
1995	9.05056759216872
1996	9.41660113339355
1997	9.53860766937191
1998	8.47175088378781
1999	8.15131325204181
2000	7.89024747645835
2001	7.98998625217315
2002	8.05058623339261
2003	8.41154688869855
2004	8.28746756605367
2005	8.60685451648519
2006	8.87166099123918
2007	9.479224713209
2008	9.85430382580397
2009	9.53814242313717
2010	9.64290426662776
2011	10.6280512913985
2012	10.8616110332145
2013	11.1735673964525
2014	11.3168512326783