Year	constant 2021 PPP $ per kg of oil equivalent
1990	6.16900428802971
1991	6.221784681683921
1992	6.384571872011074
1993	6.483394148460636
1994	6.629929717057733
1995	6.606691153462516
1996	6.831909646984318
1997	7.022045637192403
1998	7.169825575626833
1999	7.264537010464503
2000	7.470364802104186
2001	7.5360707883417195
2002	7.5656456262724
2003	7.458051781559251
2004	7.407171806091419
2005	7.458375639965314
2006	7.598104857280626
2007	7.788467184763124
2008	7.9344889831461
2009	7.916290312790567
2010	7.9604739399949676
2011	8.066365629732843
2012	8.190851720334578
2013	8.411805386706725
2014	8.620195797620681