Year	US$ per liter
1991	0.68
1992	0.62
1995	0.56
1998	0.59
2000	0.615
2002	0.66
2004	0.88
2006	1.0350000000000001
2008	1.14
2010	1.245
2012	1.355
2014	1.32
2016	0.95