Year	constant 2011 PPP $ per kg of oil equivalent
1991	5.73443146277973
1992	6.06517707025105
1993	5.89535304839571
1994	6.26619688211512
1995	6.12315693329606
1996	5.96790284140924
1997	6.29135505752924
1998	6.63905347308583
1999	6.90176242127807
2000	7.33637355839795
2001	7.43951201351629
2002	7.77542402894444
2003	7.9093529812936
2004	8.32657628954624
2005	8.22534471434325
2006	8.61150087747136
2007	8.84122097282667
2008	9.00457549359689
2009	8.96212684445981
2010	8.72153475154244
2011	9.1353098511741
2012	9.54741143021034
2013	10.176883957803
2014	10.4399134880669
2015	10.3081747675333