| 时间 | 值 （亿美元） | 世界排名 |
|---|---|---|
| 2015 | 1.6 | 142 |
| 2014 | 0.4 | 166 |
| 2013 | 0.4 | 165 |
| 2012 | 0.5 | 169 |
| 2011 | 0.6 | 166 |
| 2010 | 0.5 | 167 |
| 2009 | 2 | 125 |
| 2008 | 0.5 | 169 |
| 2007 | 1.9 | 142 |
| 2006 | 2.4 | 128 |
| 2005 | 2.7 | 111 |
| 2004 | 1.9 | 115 |
| 2003 | 0.6 | 139 |
| 2002 | 0.5 | 132 |
| 2001 | 0 | 168 |
| 2000 | 0 | 168 |
| 1999 | 0.1 | 153 |
| 1998 | 0 | 176 |
| 1997 | 0 | 177 |
| 1996 | 0 | 162 |
| 1995 | 0 | 168 |
| 1994 | 0 | 156 |
| 1993 | 0 | 157 |
| 1992 | 0 | 143 |
| 1991 | 0 | 140 |
| 1987 | 0 | 121 |