Year	constant 2021 PPP $ per kg of oil equivalent
1990	8.78737977399482
1991	8.565964711018788
1992	8.602296879605916
1993	8.72592350857467
1994	8.488191885316736
1995	8.538281059092302
1996	8.215023869001673
1997	8.526103339731216
1998	8.551432763331608
1999	8.819079891494912
2000	9.033534518173791
2001	9.158279812844691
2002	9.691793510699018
2003	9.403804869624357
2004	9.692435954345767
2005	9.929416437482049
2006	10.273318359633569
2007	10.83766385242175
2008	10.567383456157229
2009	10.780967799919726
2010	10.308700018622222
2011	11.256523274407115
2012	11.843697839531563
2013	11.482015990091766
2014	12.324941818504339
2015	12.558391553703979