Year	constant 2021 PPP $ per kg of oil equivalent
1990	10.273729207383655
1991	9.787490128223359
1992	9.382061220895768
1993	8.348754113360801
1994	8.220216655866544
1995	8.312877871232173
1996	8.454439867501103
1997	8.592553541478594
1998	8.74645576243728
1999	9.070679197138782
2000	9.031683274423155
2001	9.312302918221024
2002	9.504085377344355
2003	9.630959285148874
2004	9.998347300877228
2005	10.160718038589794
2006	11.067909991715005
2007	12.245036957448077
2008	12.484482208256647
2009	11.845500493289853
2010	12.096558675649892
2011	12.97565437904455
2012	13.16422741133279
2013	13.152923327335106
2014	13.307931325584358