Year	constant 2011 PPP $ per kg of oil equivalent
1990	5.66421961196283
1991	5.72149809657233
1992	5.63987896707928
1993	5.5974547577035
1994	5.82433565042559
1995	5.92910412551697
1996	5.78074918804643
1997	5.86057869694992
1998	5.97345513978607
1999	6.14252418816667
2000	6.27076226736483
2001	6.5344156502337
2002	6.56558257453243
2003	6.67975333091329
2004	6.83454532148834
2005	7.00359511232487
2006	6.91340282476779
2007	6.94115995627606
2008	6.93842608498775
2009	7.04921595720734
2010	7.168816273006
2011	7.30437988134957
2012	7.68530328149046
2013	7.90328600742066
2014	8.18645478830159
2015	8.03340738487966