Year	constant 2011 PPP $ per kg of oil equivalent
1990	3.79826678396485
1991	3.60534687897017
1992	3.78775587537119
1993	3.83653020366319
1994	4.23855151654108
1995	4.38416933505457
1996	4.46834688199776
1997	4.82036927520722
1998	5.41663619923122
1999	5.8178905133068
2000	6.34919737573527
2001	6.38596934418214
2002	6.58203349106314
2003	6.64648062198989
2004	6.96829186597392
2005	7.12194774957318
2006	7.20053710840983
2007	7.740460138987
2008	7.95075463489292
2009	8.49486464432865
2010	8.24570458463768
2011	8.61182157075369
2012	9.04634279790938
2013	9.18102935194296
2014	9.84690164239684
2015	10.162709303617