Year	constant 2011 PPP $ per kg of oil equivalent
1990	8.49940757261315
1991	8.96080786649269
1992	9.21175031637562
1993	9.58047746530147
1994	9.35895127596312
1995	9.48775147297615
1996	9.14847902370774
1997	8.77691265126804
1998	8.84287703271445
1999	8.28845310110068
2000	8.68145872821201
2001	9.1390110584485
2002	9.10225946523585
2003	9.3771546367301
2004	9.43998614593579
2005	9.68211213920697
2006	9.88944081015187
2007	10.0022942334739
2008	10.4554748551812
2009	10.5730331386426
2010	10.7102453685247
2011	10.4308126302935
2012	9.92338905434786
2013	9.92792801266878
2014	10.8286067891806
2015	11.0978535878742