Year	constant 2011 PPP $ per kg of oil equivalent
1990	3.16380430967564
1991	3.14976824323445
1992	2.77530637843046
1993	2.93144647696771
1994	3.22530165379253
1995	3.17293192192737
1996	3.51645755681738
1997	3.64700101331337
1998	3.66690109143036
1999	3.41029873796253
2000	3.49728453069492
2001	3.55721260674429
2002	3.29874139302168
2003	2.86309510186899
2004	2.76018716710676
2005	2.47990513065596
2006	2.3382334168815
2007	2.29852413286736
2008	2.03666392350661
2009	2.23889055905006
2010	2.58817676327433
2011	2.72699580336666
2012	3.01712982955402
2013	2.94742204491005