Year	U.S. dollars (Units)
1980	486.908
1981	339.389
1982	239.807
1983	318.513
1984	375.019
1985	253.184
1986	328.588
1987	516.781
1988	404.705
1989	696.391
1990	87.197
1991	95.292
1992	113.476
1993	186.506
1994	205.922
1995	239.507
1996	292.909
1997	350.723
1998	366.582
1999	352.442
2000	422.316
2001	492.676
2002	554.652
2003	635.575
2004	772.939
2005	996.677
2006	1249.767
2007	1599.596
2008	1700.513
2009	1401.244
2010	1637.419
2011	2034.461
2012	1396.292
2013	1462.582
2014	1628.497
2015	1679.025
2016	1638.638
2017	1199.177
2018	796.298
2019	777.066
2020	777.313
2021	764.872
2022	723.252
2023	536.922
2024	546.707
2025	544.379
2026	546.112
2027	542.750
2028	536.893
2029	523.605