Year	constant 2021 PPP $ per kg of oil equivalent
1990	5.7666211570101735
1991	6.0541522793956775
1992	6.134756866251961
1993	6.137562193641457
1994	6.230556026519346
1995	6.258773206014474
1996	6.41438464476215
1997	6.57738428413102
1998	6.613992935691204
1999	6.69622579429535
2000	6.826479708273262
2001	6.930753587332561
2002	6.963380351786512
2003	6.8206681571523875
2004	6.644596831337794
2005	6.687575738004178
2006	6.770900512297453
2007	6.945477645609117
2008	7.153918189791337
2009	7.128277413901771
2010	7.079836338109118
2011	7.224019598896344
2012	7.429408469194428
2013	7.627197280218047
2014	7.851712708789159