Year	constant 2011 PPP $ per kg of oil equivalent
1990	6.02746544435501
1991	6.02779928233059
1992	6.11938335733884
1993	6.12607292117038
1994	6.231238670436
1995	6.27207425914282
1996	6.29385073765684
1997	6.46292544360177
1998	6.62163326340184
1999	6.7326821849976
2000	6.8554659774513
2001	6.98238507060886
2002	7.05396656123041
2003	7.10474050018675
2004	7.19767489719023
2005	7.38773606158571
2006	7.63585075247053
2007	7.80671752750626
2008	7.93737093306866
2009	8.05449239630644
2010	7.98967555287132
2011	8.30966917098097
2012	8.49291022897059
2013	8.58677691371563
2014	8.81220492194817
2015	9.08288845156594