Year	constant 2011 PPP $ per kg of oil equivalent
1990	4.00559285168865
1991	3.79680291455038
1992	3.98388357140293
1993	3.76319295460672
1994	3.75581615440472
1995	3.67122998106341
1996	3.74708709951352
1997	3.74332743828616
1998	3.78678589052873
1999	3.83136184538345
2000	4.00044966258922
2001	3.99450599275191
2002	4.22220535563305
2003	4.0650397045098
2004	3.89274090853224
2005	4.10478144403745
2006	4.36637860159379
2007	4.29627155441677
2008	4.11580112901676
2009	4.13389892222306
2010	4.32541220964336
2011	4.48314326797993
2012	4.64732450424288
2013	4.74795147429302
2014	4.59604545519812