Year	constant 2011 PPP $ per kg of oil equivalent
1990	9.54601635455125
1991	9.42336670758562
1992	9.15792292934334
1993	8.58935333358115
1994	7.96048346390318
1995	9.80174389102206
1996	8.92562392430939
1997	9.34971846618078
1998	9.2697371287944
1999	9.68185671299404
2000	9.53800373906556
2001	10.0214561431771
2002	10.254316549159
2003	9.67238041250968
2004	10.8448443945318
2005	11.1908057178925
2006	11.2661578660551
2007	11.2098764070558
2008	10.9659157501416
2009	10.9918873378995
2010	11.5162983545786
2011	11.9265120419453
2012	12.3183578382425
2013	13.3836332108204
2014	12.9252903620835