Year	constant 2011 PPP $ per kg of oil equivalent
1990	9.63197642497956
1991	8.89128641433492
1992	9.11567440891205
1993	9.16374758709838
1994	9.05799189852888
1995	8.92192249526003
1996	9.41176398640767
1997	8.77097729043981
1998	8.75280546521842
1999	8.6175216376899
2000	8.32977910256681
2001	8.03171493020953
2002	8.00228759361758
2003	7.78554933921664
2004	7.9193655899287
2005	7.90600263415072
2006	7.85467975059082
2007	8.45731810926552
2008	8.6005526246515
2009	8.99120118583292
2010	9.13880368069318
2011	9.39669118329227
2012	9.81211199735904
2013	10.6257666873607
2014	10.6027670905001