Year	constant 2011 PPP $ per kg of oil equivalent
1990	7.10435391730989
1991	6.76811627304222
1992	6.48775941451377
1993	5.77322049207354
1994	5.6981246592294
1995	5.79460187015215
1996	5.901536535361
1997	6.03834244413711
1998	6.13339339839494
1999	6.34740667320196
2000	6.30313347984735
2001	6.50170549420506
2002	6.62037324696279
2003	6.65238812943828
2004	6.88887013225427
2005	6.98652641677495
2006	7.58451413312293
2007	8.43738135570114
2008	8.65599462132532
2009	8.18249126283182
2010	8.39842361606743
2011	9.07412690111033
2012	9.19872173460862
2013	9.22660172512867
2014	9.34984071340766