Year	US$ per liter
1991	0.71
1992	0.7
1995	0.625
1998	0.635
2000	0.68
2002	0.665
2004	0.92
2006	1.12
2008	1.22
2010	1.275
2012	1.3900000000000001
2014	1.35
2016	0.97