Year	constant 2011 PPP $ per kg of oil equivalent
1990	1.3665458335337
1991	1.3113806247358
1992	1.2368730611862
1993	1.16163101420118
1994	1.1130253234122
1995	1.20226972423216
1996	1.18241224083947
1997	1.22298561734102
1998	1.14768970847176
1999	1.1657049977878
2000	1.22094426663007
2001	1.26397048957246
2002	1.26183464394247
2003	1.3603614509194
2004	1.48291290862934
2005	1.71114300866964
2006	1.79979804331636
2007	1.98399988091757
2008	2.07568981115716
2009	2.52570873513928
2010	2.80299708146366
2011	2.76984106679186
2012	2.93050613056126
2013	3.57006926424555