Year	constant 2011 PPP $ per kg of oil equivalent
1990	5.58073238408756
1991	5.60513575792183
1992	5.69512327606703
1993	5.73097221473132
1994	5.85811661349055
1995	5.89198460577092
1996	5.96890330307975
1997	6.14836881690217
1998	6.27603274724996
1999	6.36625370424826
2000	6.51750119451091
2001	6.59254417019777
2002	6.64191298732537
2003	6.65121773844431
2004	6.70546840842529
2005	6.83484512195593
2006	6.99670732620839
2007	7.17102654809638
2008	7.27592984460488
2009	7.29774173551177
2010	7.26917239326984
2011	7.44006479586883
2012	7.54596751296824
2013	7.70039946088244
2014	7.90833796299128