Year	constant 2021 PPP $ per kg of oil equivalent
1990	6.5905776005128285
1991	6.534239675669473
1992	6.614318560031575
1993	6.723868590371565
1994	6.701237089668267
1995	6.757314936898173
1996	6.861227466343127
1997	7.0260491879842455
1998	7.031075170356154
1999	7.067870866237912
2000	7.333148579031643
2001	7.398195753313369
2002	7.3946911112852005
2003	7.555192884711795
2004	7.811279132907968
2005	7.942918570595175
2006	8.199230068583244
2007	8.437833839047816
2008	8.648947489437354
2009	8.84991058528182
2010	9.069436169319562
2011	9.24032480778093
2012	9.264445032771293
2013	9.527306382517892
2014	9.855244327240099