Year	constant 2011 PPP $ per kg of oil equivalent
1990	3.22496447936481
1991	3.4973845867115
1992	3.71681198938333
1993	3.86736013841317
1994	4.09434047168739
1995	4.17002264088484
1996	4.38397290262889
1997	4.63065935715685
1998	4.66700444058652
1999	4.82310192741393
2000	4.98050829342941
2001	5.12046302955064
2002	5.1817569798872
2003	5.03349619040652
2004	4.87470756028551
2005	4.89429219614874
2006	5.01315050278093
2007	5.227515454755
2008	5.48109963731248
2009	5.54689371410514
2010	5.54294697745819
2011	5.66549247096126
2012	5.85915332481489
2013	6.06168736436037
2014	6.32596821894888