Year	constant 2011 PPP $ per kg of oil equivalent
1990	5.30717347451835
1991	5.39964770351807
1992	5.415676128667
1993	5.41927119342736
1994	5.37996484333984
1995	5.35140119418898
1996	5.4108025054089
1997	5.39485178554312
1998	5.3440154293856
1999	5.37189319175411
2000	6.8166609713616
2001	7.04412464130979
2002	7.40585268807824
2003	8.23398999079299
2004	8.7001972675396
2005	9.29488281162153
2006	9.28294709419136
2007	9.68567217511986
2008	10.571234210657
2009	10.2336566232807
2010	10.1245575614964
2011	10.8171891803627
2012	10.9237406624962
2013	11.2044549616023
2014	11.425464709815