Year	constant 2011 PPP $ per kg of oil equivalent
1990	4.73241514977305
1991	4.69116784786986
1992	4.63217608233061
1993	4.56645575012113
1994	4.5019073398723
1995	4.56124394837818
1996	4.71202291070654
1997	4.81006554881075
1998	4.8580158994425
1999	4.89193809378824
2000	5.04808031170303
2001	5.10422021969547
2002	5.18284115334002
2003	5.26041701247514
2004	5.55002913444323
2005	5.82462237113245
2006	6.03708993254748
2007	6.35666707022795
2008	6.50547520624615
2009	6.52987996313683
2010	6.71503359578763
2011	6.77972986015528
2012	6.9379175713321
2013	7.05246411410098
2014	7.02833534278939