Year	constant 2011 PPP $ per kg of oil equivalent
1990	2.15459178015527
1991	1.97091731037948
1992	2.04566475222378
1993	1.97992097746659
1994	1.79079218072716
1995	1.59223411797623
1996	1.56418405781022
1997	1.58570560169942
1998	1.64498361187751
1999	1.64941059421385
2000	1.76327322083638
2001	1.9212219717957
2002	1.99962519564752
2003	2.05305023580775
2004	2.31430772790294
2005	2.39987411985491
2006	2.6824871505258
2007	2.84442478866359
2008	3.0117538680942
2009	3.01792049121487
2010	2.71025741527569
2011	2.9910054407249
2012	3.09713130077477
2013	3.26617097294341
2014	3.35415413370093