Year	constant 2011 PPP $ per kg of oil equivalent
1990	7.659716494069
1991	7.3231871904145
1992	7.57022706054433
1993	7.40046276873388
1994	7.87300668335676
1995	7.71767770725218
1996	7.4072965267422
1997	7.81976635984134
1998	7.8715372826227
1999	8.15427185020982
2000	8.39205142233221
2001	8.27529410591823
2002	8.34900178409346
2003	8.26926777139695
2004	8.38047495867573
2005	8.48463620886992
2006	8.83465803944201
2007	9.15326869860078
2008	9.13643431772049
2009	9.27307929995034
2010	9.16512689211859
2011	9.7322409175987
2012	9.74195488718917
2013	9.75573054155717
2014	10.2697992589026
2015	10.2549464372932