Year	constant 2021 PPP $ per kg of oil equivalent
1990	3.612070864930532
1991	3.912862950499395
1992	4.155143746986383
1993	4.320484779189198
1994	4.570526317292062
1995	4.653825691302364
1996	4.890307452802162
1997	5.159272801601843
1998	5.197991876587759
1999	5.3708984881602575
2000	5.543421723517303
2001	5.696244477311995
2002	5.762118913391029
2003	5.595141187810001
2004	5.416127907228441
2005	5.432431881953956
2006	5.5573644089249195
2007	5.787735957035202
2008	6.064623051069356
2009	6.130644461712436
2010	6.1225120791633705
2011	6.253132900768092
2012	6.466341304536327
2013	6.686006392790447
2014	6.907714029177459