| 时间 | 值 （亿美元） | 世界排名 |
|---|---|---|
| 2016 | 1 | 114 |
| 2015 | 1 | 121 |
| 2014 | 1.1 | 124 |
| 2013 | 1 | 125 |
| 2012 | 1.1 | 122 |
| 2011 | 0.9 | 120 |
| 2010 | 0.5 | 129 |
| 2009 | 0.4 | 134 |
| 2008 | 0.7 | 126 |
| 2007 | 0.6 | 126 |
| 2006 | 0.4 | 133 |
| 2005 | 0.3 | 140 |
| 2004 | 0.3 | 139 |
| 2003 | 0.2 | 139 |
| 2002 | 0.3 | 130 |
| 2001 | 0.2 | 129 |
| 2000 | 0.2 | 126 |
| 1999 | 0.2 | 129 |
| 1998 | 0.2 | 128 |
| 1997 | 0.2 | 131 |
| 1996 | 0.2 | 127 |
| 1995 | 0.2 | 123 |
| 1994 | 0.2 | 126 |
| 1993 | 0.1 | 129 |
| 1992 | 0.3 | 108 |
| 1991 | 0.9 | 85 |
| 1990 | 1.2 | 82 |
| 1989 | 2.8 | 60 |
| 1988 | 3 | 58 |
| 1987 | 2.6 | 58 |