Year	constant 2021 PPP $ per kg of oil equivalent
1990	3.0945754599351614
1991	3.053041406761719
1992	3.342766433783453
1993	3.8050581844654534
1994	3.7082022178321634
1995	4.085190120481502
1996	3.9001220773710723
1997	4.495677184613613
1998	5.140743308158257
1999	5.446386285152134
2000	6.122563265299279
2001	6.22397763344689
2002	6.933819815128372
2003	6.7521527473808955
2004	7.077125956831563
2005	7.891071702084063
2006	8.877602150559039
2007	8.534667164790854
2008	8.39175543495453
2009	8.075810082769992
2010	7.165417232703341
2011	7.681942680179332
2012	8.079125656721422
2013	7.427467993242886
2014	7.722445236088097
2015	8.650114635783835