Year	constant 2021 PPP $ per kg of oil equivalent
1990	5.224453969830289
1991	5.12781316093007
1992	5.055864637738227
1993	5.021953873110924
1994	5.068698148938606
1995	5.1364562090268855
1996	5.121684300105173
1997	5.286255999274087
1998	5.520555475924262
1999	5.644384131628602
2000	5.767328751747428
2001	5.962570799908639
2002	6.122455128228305
2003	5.919807976585346
2004	5.964531526275418
2005	6.1224177999252385
2006	6.3582221855611145
2007	6.446629052850062
2008	6.455220438782892
2009	6.511973013775073
2010	6.64631364682988
2011	6.682532810264921
2012	6.881367260495418
2013	6.9581276369585705
2014	6.948169656440181
2015	7.183747426139276