Year	constant 2011 PPP $ per kg of oil equivalent
1994	4.39087468456032
1995	4.47875514073997
1996	4.66053363317877
1997	5.18212626719957
1998	5.6504784803683
1999	6.31054271571826
2000	6.90479959447305
2001	6.85090837955045
2002	7.40603085639502
2003	7.5648315006548
2004	7.98473031503209
2005	8.66338329319288
2006	9.36088423629041
2007	10.0646446613368
2008	10.152231554601
2009	9.05199465894907
2010	8.49459182143985
2011	9.56789138528712
2012	9.59551578231483
2013	10.0009644904707
2014	10.1854970914867