Year	constant 2021 PPP $ per kg of oil equivalent
1990	8.496454217212369
1991	8.481957958371005
1992	8.585398351707273
1993	8.559330487383026
1994	8.58601186721652
1995	8.500974505825523
1996	8.73905471663713
1997	8.804056827569582
1998	8.775317998432033
1999	8.674833873830208
2000	8.865123478830379
2001	8.844024270048486
2002	8.802526635565133
2003	9.02268754131776
2004	9.13899738312392
2005	9.306517488700038
2006	9.454683258072654
2007	9.649498827030934
2008	9.600726249192315
2009	9.411487336407582
2010	9.701470138804797
2011	10.010984904789947
2012	9.998042722082092
2013	10.330970898610556
2014	10.424210779711458