Year	constant 2021 PPP $ per kg of oil equivalent
1990	5.874125357143079
1991	5.867801867778286
1992	5.951848442424051
1993	6.022168293103003
1994	6.201809620310975
1995	6.205929939176538
1996	6.378735270176732
1997	6.603511227063877
1998	6.7330342603293785
1999	6.831880728712715
2000	7.070907270090535
2001	7.158008093276491
2002	7.237681370185194
2003	7.189899464505114
2004	7.235416122535299
2005	7.331209698447091
2006	7.496413574512698
2007	7.741879650274284
2008	7.902909349735051
2009	7.89052071663986
2010	7.9094830268138825
2011	8.005304666545074
2012	8.1270475971248
2013	8.349741741439304
2014	8.572480050053677