Year	constant 2021 PPP $ per kg of oil equivalent
1990	10.07045560451591
1991	9.830582921010578
1992	9.455349919207254
1993	8.957733285303746
1994	8.580838630175107
1995	8.555015476501136
1996	8.799630755275409
1997	8.64421644001971
1998	8.935576713008091
1999	8.83112660712804
2000	9.29020238044959
2001	8.788859797390135
2002	8.582535972487229
2003	8.772538287998582
2004	8.860970367542093
2005	8.655874118612992
2006	8.603735306286596
2007	8.624376203334464
2008	8.395589451720749
2009	8.210470031895825
2010	8.244613822003386
2011	8.498075175921304
2012	8.161516782124112
2013	8.319327711882297
2014	8.153797663957787