Year	constant 2011 PPP $ per kg of oil equivalent
1990	7.66795012672781
1991	7.85644043087326
1992	7.94425413000405
1993	7.69300763236271
1994	7.66557796934129
1995	7.70358568272397
1996	7.67469942225466
1997	7.55176726547141
1998	7.58028509447456
1999	7.44195727469947
2000	7.55705771975092
2001	7.5831632560425
2002	7.74071123072001
2003	7.76352092766141
2004	7.77525825055415
2005	8.07334960035297
2006	8.2286038352621
2007	8.18753454637621
2008	8.46900113963815
2009	8.57980432566946
2010	8.59339098326867
2011	8.76364162666144
2012	8.96725458995877
2013	9.13972942369075
2014	9.44632507725673