Year	constant 2011 PPP $ per kg of oil equivalent
1990	7.76279599754377
1991	7.43294453962943
1992	6.24175614142112
1993	5.62556987172548
1994	6.19565604530503
1995	6.06236834656656
1996	5.19005506993935
1997	5.78951715343749
1998	5.56596606518787
1999	6.19102504188893
2000	6.57543409525874
2001	6.59899254255731
2002	6.82829792519717
2003	6.3236474108465
2004	6.72347179083993
2005	6.9046181039972
2006	6.93326913203699
2007	7.15547673241081
2008	7.558800230573
2009	8.08085023375879
2010	8.16617960243524
2011	7.70967405016673
2012	8.08920073463987
2013	9.12950362271674
2014	9.74090115547766