Year	US$ per liter
1991	0.5700000000000001
1992	0.58
1995	0.525
1998	0.48
2000	0.47
2002	0.545
2004	0.8200000000000001
2006	1
2008	1.14
2010	1.135
2012	1.26
2014	1.2
2016	0.88