Year	constant 2021 PPP $ per kg of oil equivalent
1990	3.6120772635301974
1991	3.912862950499395
1992	4.155143746986384
1993	4.320484779189197
1994	4.570526317292063
1995	4.653825691302364
1996	4.890307452802162
1997	5.159272801601843
1998	5.197991876587759
1999	5.370898488160257
2000	5.5434217235173024
2001	5.696244477311997
2002	5.762118913391028
2003	5.595141187810001
2004	5.416127907228442
2005	5.432431881953955
2006	5.557364408924919
2007	5.787735957035202
2008	6.064623051069356
2009	6.130644461712436
2010	6.12251207916337
2011	6.253132900768092
2012	6.466341304536327
2013	6.686006392790447
2014	6.907714029177459