Year	constant 2011 PPP $ per kg of oil equivalent
1990	2.9047214092236
1991	2.53354305650225
1992	2.28066330251654
1993	2.48805039039179
1994	2.45452751604352
1995	2.50750106410309
1996	2.90291966224046
1997	3.39016570145761
1998	3.33905056576445
1999	3.75528733184511
2000	4.15132413328282
2001	4.8672913528694
2002	4.64523080579103
2003	4.68066266532797
2004	4.35361876387255
2005	4.76762296351274
2006	4.37135940335804
2007	4.4248533138006
2008	4.32386966849097
2009	4.81605135464397
2010	4.74551748329294
2011	4.55528759502616
2012	4.99808974113917
2013	4.79932821888412
2014	5.31888545388371