Year	constant 2011 PPP $ per kg of oil equivalent
1990	4.6438974834878
1991	4.6764835894046
1992	4.78565076227183
1993	4.88341774994813
1994	5.04297313915544
1995	5.07117503260875
1996	5.23481949098446
1997	5.42492860175507
1998	5.52353724396518
1999	5.60887997104681
2000	5.78978901241368
2001	5.85985005110647
2002	5.92370631518278
2003	5.88796456694167
2004	5.93113207442758
2005	6.03134273791333
2006	6.17595476069691
2007	6.39385712596442
2008	6.52778193365104
2009	6.55161873386462
2010	6.57335108613362
2011	6.65440682831514
2012	6.76207389298469
2013	6.9707826187266
2014	7.17916906201211