Year	constant 2011 PPP $ per kg of oil equivalent
1990	3.32661602197397
1991	3.75893480212028
1992	3.64524586243606
1993	3.90393812153585
1994	3.66355788875724
1995	3.76005970535892
1996	3.91591364522494
1997	3.58126318201419
1998	3.5718943815702
1999	3.7600506080999
2000	3.74872081849878
2001	3.73884182513076
2002	3.73618320834252
2003	3.73384326607914
2004	3.97939000603897
2005	3.70023999145123
2006	3.67736675462675
2007	3.80582010036259
2008	3.72992188397561
2009	3.93798373058502
2010	3.97444416021251
2011	4.05220016120827
2012	4.24126759686817
2013	4.09725086269059
2014	4.13794184253685