Year	2007 US$
1961	35.31
1962	27.14
1963	27.65
1964	29.41
1965	28.88
1966	29.19
1967	28.26
1968	32.94
1969	37.91
1970	39.43
1971	41.23
1972	42.61
1973	42.59
1974	60.21
1975	101.7
1976	82.37
1977	71.04
1978	60.43
1979	66.23
1980	63.27
1981	56.7
1982	56.41
1983	54.43
1984	53.64
1985	52.62
1986	59.75
1987	53.42
1988	53.18
1989	46.42
1990	48.81
1991	50.74
1992	51.84
1993	49.91
1994	49.88
1995	48.58
1996	44.08
1997	56.93
1998	58.45
1999	60.36
2000	57.77
2001	58.73
2002	56.25
2003	58.96
2004	62.97
2005	74.56
2006	73.26
2007	75.78