Year	constant 2021 PPP $ per kg of oil equivalent
1990	8.06482964280897
1991	8.066586620170439
1992	8.157970849157238
1993	8.148165469481636
1994	8.263954153410458
1995	8.30409743869398
1996	8.31696220501548
1997	8.541720270426934
1998	8.765975131172963
1999	8.89947173284153
2000	9.067545806651164
2001	9.218356327452405
2002	9.301174846181082
2003	9.36548948953321
2004	9.496622797406905
2005	9.707396630349542
2006	10.00507789652305
2007	10.22968609511154
2008	10.404259518077316
2009	10.495156964211283
2010	10.466581530708389
2011	10.883365259244792
2012	11.100908047050648
2013	11.226163672817295
2014	11.551034883227093
2015	11.765646097863888