Year	constant 2021 PPP $ per kg of oil equivalent
1990	6.073201620729654
1991	5.953598569000631
1992	6.02253573070702
1993	5.962343887873142
1994	5.996752838531904
1995	6.093055761313055
1996	6.155832279596554
1997	6.218461845397678
1998	6.198628961591687
1999	6.165426378906548
2000	6.337193525732889
2001	6.422100854994634
2002	6.544042753379796
2003	6.685461358833368
2004	6.993563600415786
2005	7.223474708670461
2006	7.470605357304888
2007	7.679113296607605
2008	7.826296636766204
2009	8.208357923406066
2010	8.382080565862644
2011	8.453314330245066
2012	8.49951953043987
2013	8.865296057440254
2014	9.651327644784747