Year	constant 2021 PPP $ per kg of oil equivalent
1990	6.753311372339101
1991	6.177138770142923
1992	5.429259861636504
1993	4.605811944794387
1994	4.410259839744337
1995	4.2604879182427045
1996	4.078293667910661
1997	3.782723239482649
1998	3.6323535627621255
1999	3.4630577413672032
2000	3.2204431292267697
2001	3.0503831213341925
2002	3.0348541061039476
2003	3.0889363004069614
2004	3.1706771110388865
2005	3.2398759860777613
2006	3.2877435920340674
2007	3.370855527599771
2008	3.4532276434180527
2009	3.4483385746439796
2010	3.562317131156113
2011	3.584907367924409
2012	3.0941501827622364
2013	3.1939166820078553
2014	3.346063773790523