Year	US$ per liter
1991	0.58
1992	0.5700000000000001
1995	0.48
1998	0.45
2000	0.47
2002	0.5
2004	0.8
2006	1
2008	1.05
2010	1.11
2012	1.22
2014	1.17
2016	0.88