| 时间 | 值 （亿美元） | 世界排名 |
|---|---|---|
| 2015 | 1.5 | 144 |
| 2014 | 1.5 | 145 |
| 2013 | 1.3 | 143 |
| 2012 | 1.3 | 153 |
| 2011 | 0.7 | 163 |
| 2010 | 1 | 156 |
| 2009 | 0.8 | 151 |
| 2008 | 1.6 | 150 |
| 2007 | 3.4 | 130 |
| 2006 | 3.6 | 110 |
| 2005 | 2.2 | 119 |
| 2004 | 0.8 | 132 |
| 2003 | 1.7 | 106 |
| 2002 | 0.7 | 124 |
| 2001 | 1 | 109 |
| 2000 | 0.4 | 129 |
| 1999 | 0.5 | 126 |
| 1998 | 0.2 | 140 |
| 1997 | 0.2 | 139 |
| 1996 | 0.2 | 128 |
| 1995 | 0.3 | 115 |
| 1994 | 0.2 | 110 |
| 1993 | 0.2 | 117 |
| 1992 | 0.2 | 98 |
| 1991 | 0.5 | 69 |
| 1990 | 0.6 | 65 |
| 1989 | 0.4 | 64 |
| 1988 | 0.3 | 67 |
| 1987 | 0.4 | 65 |
| 1986 | 0.2 | 60 |