Year	constant 2021 PPP $ per kg of oil equivalent
1990	9.972394837057024
1991	9.540524197818225
1992	9.285423343475513
1993	8.739857079093213
1994	8.332152222452748
1995	8.265071489984377
1996	8.76454040880705
1997	8.342240696029847
1998	8.975448329621877
1999	8.983023185219242
2000	9.547839842537297
2001	9.138330179815421
2002	9.172262232571866
2003	9.132794084380595
2004	9.164880998549584
2005	8.727836135511778
2006	8.874151736172806
2007	8.993227119430868
2008	8.854392887749873
2009	8.852253065463316
2010	9.198040422092934
2011	9.178655448670813
2012	8.983793261983653
2013	8.941694609961088
2014	8.795855506352467