Year	constant 2021 PPP $ per kg of oil equivalent
1990	7.739526654791259
1991	7.724081894726789
1992	7.834774086707979
1993	7.8263297129036085
1994	7.946535730133928
1995	7.989471254657265
1996	8.008137361955722
1997	8.218073654160007
1998	8.421500406618314
1999	8.559086555237112
2000	8.718510564952167
2001	8.885221256381662
2002	8.97013000482315
2003	9.032409783476787
2004	9.154325972548525
2005	9.392028539304478
2006	9.708485458539101
2007	9.933589032770787
2008	10.11203783233112
2009	10.244473212733654
2010	10.170975266074151
2011	10.585533263224928
2012	10.812182028855085
2013	10.936462279321786
2014	11.213429212546147
2015	11.488229894715044