Year	US$ per liter
1991	0.5800000000000001
1992	0.51
1995	0.52
1998	0.44999999999999996
2000	0.56
2002	0.52
2004	0.88
2006	1.04
2008	1.2149999999999999
2010	1.2850000000000001
2012	1.47
2014	1.375
2016	0.95