Year	constant 2011 PPP $ per kg of oil equivalent
1990	6.39651128580288
1991	6.39640259805734
1992	6.45041896126681
1993	6.43926804583699
1994	6.52685092406706
1995	6.55046835119162
1996	6.56578935334271
1997	6.74101061645199
1998	6.91503560954908
1999	7.02038153533013
2000	7.15109551365311
2001	7.26608800283024
2002	7.33768666486318
2003	7.39311915876138
2004	7.49828150432412
2005	7.66949451716145
2006	7.9061217653811
2007	8.07825188390406
2008	8.20915587379397
2009	8.28981173051627
2010	8.26184462610807
2011	8.58653864162165
2012	8.76173810201152
2013	8.86148557453817
2014	9.11670965454756
2015	9.35494309378731