Year	2011 U.S. Dollars
1975-01-01	19.46
1976-01-01	19.74
1977-01-01	20.24
1978-01-01	20.96
1979-01-01	22.26
1980-01-01	23.04
1981-01-01	22.98
1982-01-01	23.60
1983-01-01	24.46
1984-01-01	25.19
1985-01-01	25.98
1986-01-01	27.07
1987-01-01	27.77
1988-01-01	28.80
1989-01-01	30.04
1990-01-01	30.91
1991-01-01	31.17
1992-01-01	32.27
1993-01-01	33.99
1994-01-01	35.34
1995-01-01	36.08
1996-01-01	36.86
1997-01-01	37.95
1998-01-01	39.36
1999-01-01	39.82
2000-01-01	41.42
2001-01-01	42.23
2002-01-01	42.77
2003-01-01	43.79
2004-01-01	45.30
2005-01-01	46.19
2006-01-01	47.55
2007-01-01	49.09
2008-01-01	48.51
2009-01-01	45.98
2010-01-01	47.42
2011-01-01	48.08