Year	constant 2011 PPP $ per kg of oil equivalent
1990	9.58888164542787
1991	9.45746235524918
1992	8.85592564845999
1993	6.50015524173417
1994	6.49837593761435
1995	7.4791055606423
1996	8.25266223656126
1997	8.66429574655666
1998	9.0936946712153
1999	8.84655390459683
2000	8.87542299490146
2001	8.85892472839406
2002	9.625048815115
2003	9.18627850272379
2004	9.90658197559943
2005	11.7917737852621
2006	11.9884753511104
2007	12.8138472918877
2008	13.1598736325769
2009	12.2133652407238
2010	12.2090240014982
2011	12.1629553353575
2012	12.0302735736372
2013	12.6104112142749
2014	12.5099806929408