Year	US$ per liter
1991	0.55
1992	0.54
1995	0.46
1998	0.43
2000	0.46499999999999997
2002	0.53
2004	0.79
2006	0.985
2008	1.065
2010	1.145
2012	1.27
2014	1.17
2016	0.855