Year	constant 2011 PPP $ per kg of oil equivalent
1990	8.65306524579725
1991	8.61542837118126
1992	8.26838346768444
1993	8.44968655553264
1994	8.23104664984448
1995	8.22460613309121
1996	8.4176942923998
1997	8.41318303108165
1998	8.13081550859786
1999	8.16504695826545
2000	8.23818031797151
2001	8.85267665250288
2002	9.05170466908225
2003	9.47739455225537
2004	10.1445780510447
2005	10.611680501344
2006	11.2503481665063
2007	11.9707083143472
2008	12.0144892295014
2009	12.7629808140852
2010	12.9853924317135
2011	13.371393624775
2012	13.4116081950761
2013	13.8653484969436
2014	13.8288060936531