Year	constant 2011 PPP $ per kg of oil equivalent
1990	6.34481602540159
1991	6.62691468541359
1992	6.41878470366558
1993	7.00235403414665
1994	6.96325841676471
1995	6.69597782696576
1996	6.34632875504167
1997	6.27441809049169
1998	5.89628433351428
1999	5.79625478645891
2000	5.5277290248198
2001	5.58461901043145
2002	6.10831884263509
2003	6.07817908391538
2004	6.08867108354657
2005	6.21827639158554
2006	5.71063430767224
2007	5.75973064222823
2008	6.78977760281704
2009	7.57260860337508
2010	8.42790555967346
2011	8.03699029924891
2012	8.22635835613585
2013	7.95665452713773
2014	8.20895808272901