Year	US$ per liter
1991	0.61
1992	0.615
1995	0.55
1998	0.49
2000	0.46499999999999997
2002	0.54
2004	0.8200000000000001
2006	1.01
2008	1.1
2010	1.135
2012	1.25
2014	1.25
2016	0.89