Year	constant 2021 PPP $ per kg of oil equivalent
1990	5.702680995739978
1991	5.509534109914047
1992	5.497213352343421
1993	5.246420770141475
1994	5.221699422436181
1995	5.20021375041511
1996	5.307877155437835
1997	5.382641671368427
1998	5.441362824056662
1999	5.37537824968967
2000	5.527289759961838
2001	5.54867420479551
2002	5.796533684559919
2003	5.761176627803101
2004	5.9026716734571245
2005	6.122773417665943
2006	6.38531622187013
2007	6.512351662274492
2008	6.4491903109755295
2009	6.605616979129444
2010	6.7973218657101535
2011	6.89454909864096
2012	6.939766467152296
2013	7.141855251752747
2014	7.350387470980332