Year	constant 2011 PPP $ per kg of oil equivalent
1990	4.17414641431845
1991	4.07887631985475
1992	4.1758313766755
1993	4.30983715867828
1994	4.57467931822071
1995	4.79393900079863
1996	4.84183780332398
1997	4.78145356980661
1998	4.92012929884918
1999	5.35825860797141
2000	5.31436738817484
2001	5.32514486456919
2002	5.35546822442779
2003	5.30276960784912
2004	5.43322527450491
2005	5.85819557931039
2006	6.1167824638466
2007	6.45431261977843
2008	6.7825116394802
2009	6.89104204267616
2010	6.6903351193028
2011	7.06276752538004
2012	7.03664047626225
2013	7.11273363179551
2014	7.43774503560443
2015	7.9288593313198