Year	constant 2021 PPP $ per kg of oil equivalent
1990	7.03470465423146
1991	6.908276069644724
1992	7.0242299915054796
1993	7.1261328200743375
1994	7.277459728559782
1995	7.363501023036983
1996	7.60810312161899
1997	7.603681367591663
1998	7.833775975329891
1999	7.984475606697011
2000	8.102437109593088
2001	8.328495120970192
2002	8.402453437668074
2003	8.760701726382921
2004	8.959589034138165
2005	9.284505004350725
2006	9.513506391101169
2007	9.666388969136701
2008	9.59153758182534
2009	9.436178770876133
2010	9.715200215831247
2011	9.831361367907496
2012	9.914345420543203
2013	10.283930758674238
2014	10.402649504108942