Year	constant 2021 PPP $ per kg of oil equivalent
1990	6.661216467602536
1991	6.623756371519629
1992	6.513910790071542
1993	6.343944541881218
1994	6.221125471523233
1995	6.298468879537444
1996	6.4949687593612415
1997	6.679521517374534
1998	6.722098873467669
1999	6.777721228715364
2000	6.993908034025782
2001	7.079600667167499
2002	7.166581401673665
2003	7.275103929755402
2004	7.6595512021597285
2005	8.012224924167459
2006	8.27209474740648
2007	8.657783285568348
2008	8.911375437769125
2009	8.901253526210446
2010	9.097797660206759
2011	9.229892289929687
2012	9.200956284714792
2013	9.40793901149575
2014	9.718048789006879