| 时间 | 值 （亿美元） | 世界排名 |
|---|---|---|
| 2013 | 0.2 | 143 |
| 2012 | 0.2 | 142 |
| 2011 | 0.2 | 138 |
| 2010 | 0.2 | 142 |
| 2009 | 0.1 | 143 |
| 2008 | 0.2 | 147 |
| 2007 | 0.1 | 141 |
| 2006 | 0.1 | 143 |
| 2005 | 0.1 | 146 |
| 2004 | 0.1 | 146 |
| 2003 | 0.1 | 145 |
| 2002 | 0.1 | 139 |
| 2001 | 0.1 | 134 |
| 2000 | 0.1 | 132 |
| 1999 | 0.2 | 131 |
| 1998 | 0.3 | 117 |
| 1997 | 0.7 | 105 |
| 1996 | 0.8 | 98 |
| 1995 | 1 | 89 |
| 1994 | 1.2 | 85 |
| 1993 | 1.1 | 88 |
| 1992 | 1 | 84 |