Year	constant 2021 PPP $ per kg of oil equivalent
1990	6.121213645271872
1991	6.167971448176742
1992	6.326421889267127
1993	6.422678093422313
1994	6.561518585475732
1995	6.54110699689406
1996	6.762921341169862
1997	6.951260031173854
1998	7.091904786395483
1999	7.18138396404491
2000	7.385996799882199
2001	7.450082181520944
2002	7.479460753558284
2003	7.381057131514109
2004	7.339790591517683
2005	7.391035816279082
2006	7.531490500561616
2007	7.723223708718826
2008	7.868436775941133
2009	7.853399422169982
2010	7.90320972227302
2011	8.011572574530463
2012	8.129452886697157
2013	8.347239624235435
2014	8.552923334885799