Year	constant 2011 PPP $ per kg of oil equivalent
1990	4.66444538189236
1991	4.55175148547793
1992	4.63352464243775
1993	4.49328435509504
1994	4.55416596602648
1995	4.59115226304809
1996	4.64017710009278
1997	4.63162899693529
1998	4.60040489963306
1999	4.54183529296428
2000	4.63265537042239
2001	4.68237624461096
2002	4.88979725461619
2003	4.99571185419966
2004	5.2609170284178
2005	5.51675681505937
2006	5.71977868878434
2007	5.8894441692613
2008	5.97763379237675
2009	6.38672362104439
2010	6.4930947719046
2011	6.50183493571556
2012	6.56621767176503
2013	6.96371742501202
2014	7.97613724152425