Year	constant 2021 PPP $ per kg of oil equivalent
1990	6.977825949431664
1991	6.214781442132353
1992	5.950160454050498
1993	5.603315954842254
1994	5.462217175334332
1995	5.554575219979006
1996	5.6987509312738664
1997	5.770044035270123
1998	6.484990587257167
1999	6.745914592554251
2000	6.891704391109112
2001	6.819789973116023
2002	6.984669232365155
2003	6.641192623304166
2004	7.3103066608010305
2005	7.497880428006524
2006	7.832576043358485
2007	8.06357560495462
2008	8.142402314715737
2009	8.229854156407667
2010	8.2276910353937
2011	8.132719612651867
2012	8.041886414581132
2013	8.275813048542673
2014	8.569422051680037