Year	constant 2011 PPP $ per kg of oil equivalent
1990	9.23943324294537
1991	9.3666682969506
1992	9.15036577932502
1993	8.58710334889343
1994	7.61790100020801
1995	7.44481398767065
1996	8.11747840877139
1997	7.28828017326406
1998	7.31247372504012
1999	6.50130404983418
2000	7.06110151219055
2001	6.55889020791958
2002	6.80198286570349
2003	7.15693331230579
2004	6.84978286462623
2005	6.36901676218122
2006	6.39861214106294
2007	6.54074441068215
2008	6.11875940808036
2009	6.1922718608216
2010	6.54951682824259
2011	6.59268924158168
2012	5.86443638794107
2013	5.74138676333828
2014	5.59757042973614