Year	constant 2021 PPP $ per kg of oil equivalent
1990	6.9029426243755285
1991	6.63220661646117
1992	6.552721200066098
1993	6.334665787299663
1994	6.395767443578859
1995	6.343218447996487
1996	6.332541377126041
1997	6.38918120314361
1998	6.513774388050894
1999	6.307315670288708
2000	6.491325613598828
2001	6.509841531156289
2002	6.890001694974975
2003	6.941325206263384
2004	7.2890278259555625
2005	7.3998516480494105
2006	7.670601164345609
2007	7.80624928227725
2008	7.835280676792731
2009	8.324136704265735
2010	8.330315321389138
2011	8.319187671205169
2012	8.325513622198509
2013	8.659285074927684
2014	9.099011490420622