Year	constant 2011 PPP $ per kg of oil equivalent
1990	4.26571110710559
1991	4.50489459537093
1992	4.50852574087967
1993	4.69634593197252
1994	5.1748653693361
1995	5.07608160448053
1996	5.14968007385402
1997	5.20987676299224
1998	5.58182289914497
1999	6.29317759139039
2000	6.45471140744312
2001	6.68193749080564
2002	6.81892788463382
2003	6.73312327794752
2004	7.59722490973628
2005	7.9707948148848
2006	8.3207897720298
2007	8.96250213595392
2008	9.83287458443193
2009	10.552075157576
2010	10.0972775469827
2011	10.0768739025617
2012	10.5419800309525
2013	11.9532284477761
2014	12.4410067134801