Year	constant 2011 PPP $ per kg of oil equivalent
1990	5.1642867458914
1991	5.10270193337894
1992	5.31636093789165
1993	5.41019136339831
1994	5.64949971448498
1995	5.70075959268949
1996	5.95325209659144
1997	6.03434734870053
1998	6.01312870813529
1999	6.07358807610549
2000	6.20365625426109
2001	6.35183125805044
2002	6.4415061343833
2003	6.65999974385901
2004	6.8344161303869
2005	7.07930898889225
2006	7.35232123002997
2007	7.60178224002725
2008	7.70487651688092
2009	7.797116191049
2010	7.91548294677585
2011	8.1100161099241
2012	8.22384580644303
2013	8.60142983195243
2014	8.99729875047146