Year	constant 2011 PPP $ per kg of oil equivalent
1990	4.64060635332838
1991	4.66969055347728
1992	4.78296459610446
1993	4.88119968105938
1994	5.04825728320315
1995	5.08504960257765
1996	5.24428948376699
1997	5.43909987776336
1998	5.54922448825721
1999	5.63613920787841
2000	5.82445596746998
2001	5.89311035417676
2002	5.9577166534645
2003	5.92358774838852
2004	5.97127509103298
2005	6.07053766021884
2006	6.21320004252739
2007	6.43431763202599
2008	6.57038512607025
2009	6.59869114307687
2010	6.61611050953541
2011	6.70008113538958
2012	6.80935391317767
2013	7.0157128268727
2014	7.23117707225222