Year	constant 2011 PPP $ per kg of oil equivalent
1990	10.1194238891752
1991	9.57801902713778
1992	9.21978651308972
1993	8.74942460752212
1994	8.32206266491831
1995	8.26262336249935
1996	8.79192526873986
1997	8.28402807304647
1998	9.02265750117868
1999	8.86360114853608
2000	9.27312885292851
2001	8.79637825991931
2002	8.86330495194162
2003	8.87056316969942
2004	8.89804957908222
2005	8.54490402768033
2006	8.69361147814459
2007	8.81946356607016
2008	8.63456463986062
2009	8.56186303264319
2010	8.90393059722677
2011	8.74046560470874
2012	8.47026796557747
2013	8.42341212140013
2014	8.19713419520165