Year	US Dollars
1971	-1082300000
1972	-1133500000
1973	-1030500000
1974	-922800000
1975	-1812300000
1976	-2085600000
1977	-1628200000
1978	-1788300000
1979	-1353500000
1980	-1624900000
1981	-1146400000
1982	391100000
1983	14400000
1984	-382400000
1985	431500000
1986	1472500000
1987	1344300000
1988	2093700000
1989	2312100000
1990	3583800000
1991	5418700000
1992	5663900000
1993	3404800000
1994	5098400000
1995	4994700000
1996	3883500000
1997	2559400000
1998	8475400000
1999	9602400000
2000	11422900000
2001	17751500000
2002	18187700000
2003	21425600000
2004	16182600000
2005	17638000000
2006	17488500000
2007	14745000000
2008	19025300000
2009	20155600000
2010	20847100000
2011	20205400000
2012	12339500000
2013	17358200000
2014	19981600000
2015	26157900000
2016	28536000000