Year	constant 2021 PPP $ per kg of oil equivalent
1990	3.360290547887693
1991	3.3679547189648558
1992	3.2169254089528425
1993	2.7605757648172773
1994	2.4425333380972476
1995	2.2927252073789375
1996	2.7480158270391017
1997	3.0177567523866724
1998	3.197766898597564
1999	3.692938721310647
2000	3.9697715808353884
2001	4.305998067908742
2002	4.665624919527261
2003	4.8886065616034164
2004	5.078978120388626
2005	6.188856249640912
2006	8.446297305971516
2007	11.533419896512536
2008	11.614024726954144
2009	14.167564781473754
2010	15.334566498441784
2011	14.15761438551744
2012	13.269812261450918
2013	13.849921261630906
2014	13.7916534295978