Year	constant 2015 US$
1973	4400000
1974	62460000
1975	7540000
1976	1400000
1977	2590000
1978	1590000
1979	6380000
1980	19950000
1981	23960000
1982	34750000
1983	26940000
1984	37450000
1985	41780000
1986	39530000
1987	93110000
1988	75140000
1989	92020000
1990	82750000
1991	83650000
1992	76880000
1993	70840000
1994	38840000
1995	39530000
1996	37250000
1997	32510000
1998	30420000
1999	27810000
2000	33140000
2001	21090000
2002	28860000
2003	24700000
2004	30390000
2005	38650000
2006	25450000
2007	27130000
2008	26560000
2009	26460000
2010	75270000
2011	20100000
2012	12750000
2013	3910000
2014	230000
2015	7480000
2016	6920000
2017	6760000