Year	constant 2021 PPP $ per kg of oil equivalent
1990	5.8561362623881035
1991	5.8598749510627615
1992	5.945131548791311
1993	6.027928646401308
1994	6.22203740417302
1995	6.216957267805142
1996	6.400944775924054
1997	6.642605473260819
1998	6.789502963492705
1999	6.903235203972969
2000	7.14920037980425
2001	7.236843211469629
2002	7.31184025850202
2003	7.241770591608099
2004	7.259553748228875
2005	7.341680119553338
2006	7.498852357615504
2007	7.747706964876559
2008	7.909912520759778
2009	7.8621625650340805
2010	7.868719730266735
2011	7.9668575221623
2012	8.095162038832056
2013	8.306197602481816
2014	8.489576831820997