Year	PPP $ per kg of oil equivalent
1990	3.858340125305163
1991	3.8685355294714805
1992	3.9221592905597396
1993	4.023380517455487
1994	4.219557158623867
1995	4.412116150590579
1996	4.463950510988019
1997	4.4912873439827585
1998	4.6410258487447615
1999	4.777088729973965
2000	4.85316556817855
2001	5.1095708670503805
2002	5.373353665265346
2003	5.714552118329065
2004	5.919524262699111
2005	6.270212919540037
2006	6.854925054222635
2007	7.239742704283915
2008	7.305697659184286
2009	7.532816289764053
2010	7.3877757013941565
2011	7.829051025317172
2012	7.570171788700727
2013	8.312087385971227
2014	8.191871977242899
2015	8.45942119422182