Year	constant 2021 PPP $ per kg of oil equivalent
1990	7.468782733971275
1991	7.455572332987599
1992	7.511577048525132
1993	7.495602063773298
1994	7.656512828038921
1995	7.722311651272415
1996	7.725374972576617
1997	7.964001086747843
1998	8.13496772518183
1999	8.259689692373003
2000	8.447042644026004
2001	8.570562867290702
2002	8.657409282201035
2003	8.745273455094603
2004	8.90141102962779
2005	9.144062872634075
2006	9.409613140182785
2007	9.654759384274264
2008	9.795409674978222
2009	9.867430168355629
2010	9.775550567812306
2011	10.12168679948376
2012	10.272358806985332
2013	10.424134568414592
2014	10.684738754690342
2015	11.577605218136572