Year	constant 2011 PPP $ per kg of oil equivalent
1990	6.49282610515654
1991	6.60353038674672
1992	6.70039989389979
1993	6.8851495783633
1994	7.40613503842855
1995	8.48203124503959
1996	8.47718595416755
1997	9.2094569373261
1998	10.113516508292
1999	10.5260323925381
2000	10.6410773068776
2001	10.3680997926716
2002	10.3638687171282
2003	9.98588347345623
2004	9.29005632052301
2005	9.39782197186109
2006	10.0020562419551
2007	11.1540172419991
2008	11.0192488933428
2009	11.204958179054
2010	11.0142905546417
2011	11.4201091955329
2012	11.590644182388
2013	12.3980403536051
2014	13.4598091773497
2015	14.3129987525715