Year	constant 2011 PPP $ per kg of oil equivalent
1990	3.94958128859047
1991	4.14258366814331
1992	4.19634219687915
1993	4.23397818761906
1994	4.58622494953678
1995	4.66720828636607
1996	4.71897346916253
1997	4.96001593955903
1998	5.35429684980191
1999	5.74396942726587
2000	6.05456545102518
2001	6.0795306680653
2002	6.27166955445301
2003	6.32318025235941
2004	6.699765595316
2005	6.94820228486129
2006	7.22337885075396
2007	7.70259569180696
2008	8.02233950408353
2009	8.31847929229278
2010	8.11689703494003
2011	8.39109226676576
2012	8.71931229873192
2013	9.05881981077454
2014	9.51317341116815