Year	constant 2011 PPP $ per kg of oil equivalent
1990	9.53290296715251
1991	9.72516136036877
1992	8.86781163550979
1993	8.67882135026205
1994	8.31922704031139
1995	7.75629603799014
1996	7.03683506945262
1997	6.85882813239473
1998	7.00326873605929
1999	7.09857101964056
2000	7.39711578163889
2001	7.16428142105594
2002	6.35643237831581
2003	6.6419294963227
2004	6.21246916088811
2005	4.24795520244967
2006	4.21838710037182
2007	4.16055533834871
2008	4.14236316969813
2009	4.20914044286421
2010	3.95613406613753
2011	4.03303280934431
2012	4.00433517724674
2013	4.14754984452797
2014	4.20786628322377