Year	constant 2021 PPP $ per kg of oil equivalent
1990	5.730935343531133
1991	5.674283691097162
1992	5.743801167693333
1993	5.790846444822395
1994	5.9063123964501
1995	5.988172245021169
1996	6.069824162182625
1997	6.275566844558568
1998	6.507394387295455
1999	6.640501022600413
2000	6.7267879827923664
2001	6.923361730526447
2002	6.975742411645813
2003	7.112233895567342
2004	7.2302658187498725
2005	7.444374043210982
2006	7.725642804483191
2007	7.75403809175352
2008	7.944235634628335
2009	8.127763976536928
2010	8.171024480675142
2011	8.370693183551854
2012	8.687732400803819
2013	8.76910739591492
2014	8.842477381347926
2015	9.237896564695184