Year	constant 2011 PPP $ per kg of oil equivalent
1990	3.64482891584598
1991	3.54431719532078
1992	3.07983869084734
1993	3.28830003269966
1994	3.37422322490181
1995	3.30461166732543
1996	2.85119595816236
1997	2.90891209558441
1998	2.91396915151563
1999	3.03861536998448
2000	3.42898427142104
2001	3.80687031215698
2002	4.2064198220553
2003	4.57861311695645
2004	4.67281285027327
2005	4.9929349960267
2006	5.18368935458786
2007	5.22646419335979
2008	5.92718380782913
2009	7.0864409007516
2010	7.3970631619857
2011	7.92183409826379
2012	7.91772812005935
2013	7.67192734978577
2014	7.59226503605233