Year	constant 2011 PPP $ per kg of oil equivalent
1990	5.36722464464594
1991	5.51043102159308
1992	5.27002052084303
1993	5.01965482009677
1994	5.16233691602395
1995	5.16066489434659
1996	5.11035404214643
1997	4.97203353749402
1998	5.14768067970398
1999	5.18136124754249
2000	5.18573183407441
2001	5.33810083740669
2002	5.51428334209856
2003	5.56264012330862
2004	5.67907264744068
2005	5.8468247482331
2006	6.05028182239072
2007	6.13664383330901
2008	6.17489059044184
2009	6.16006041828788
2010	6.01569289829052
2011	5.9863864733451
2012	6.05444919432405
2013	6.22147068606568
2014	6.31952098080159
2015	6.31358918276103