Year	U.S. dollars (Units)
1980	313.369
1981	316.495
1982	298.747
1983	279.719
1984	265.441
1985	340.227
1986	431.342
1987	465.181
1988	490.939
1989	474.879
1990	539.656
1991	502.896
1992	489.786
1993	418.922
1994	268.106
1995	340.988
1996	298.443
1997	285.804
1998	296.103
1999	290.990
2000	238.505
2001	242.794
2002	260.865
2003	310.302
2004	336.409
2005	356.688
2006	381.315
2007	427.313
2008	485.807
2009	482.648
2010	492.078
2011	551.028
2012	566.199
2013	380.304
2014	424.670
2015	377.476
2016	402.053
2017	450.744
2018	488.564
2019	480.167
2020	494.511
2021	525.281
2022	490.139
2023	514.097
2024	537.601
2025	559.462
2026	580.287
2027	598.990
2028	617.372
2029	637.962