Year	constant 2011 PPP $ per kg of oil equivalent
1990	3.43360736279804
1991	3.30766484353378
1992	3.25734978835412
1993	3.2749012302069
1994	3.32558959767604
1995	3.38115869187525
1996	3.43008912462185
1997	3.65633334777417
1998	3.7000055818741
1999	3.7878689581934
2000	4.03155875067184
2001	4.13810082208175
2002	4.29846209318709
2003	4.39828733109604
2004	4.69111655666991
2005	4.98212864082262
2006	5.19957340233636
2007	5.53415760515482
2008	5.70442062088508
2009	5.83106208008212
2010	5.7118148873817
2011	5.77890167116419
2012	5.91642347631919
2013	6.22753727076054
2014	6.5932747103035