Year	constant 2011 PPP $ per kg of oil equivalent
1990	4.7984403903811
1991	4.75460070797456
1992	4.82524335832734
1993	4.8727524290453
1994	4.97608830148281
1995	5.045323581343
1996	5.12185164450285
1997	5.29633671164516
1998	5.48699533504313
1999	5.59645949820622
2000	5.66737498822778
2001	5.83336713630521
2002	5.86856754123191
2003	6.02252820152671
2004	6.12509096163366
2005	6.31019292093884
2006	6.55236203575619
2007	6.56053651483963
2008	6.72398030023386
2009	6.89324676835247
2010	6.90910939144086
2011	7.09571554298132
2012	7.36782404910569
2013	7.41550956805564
2014	7.4821393476465
2015	7.81719723358152