| 时间 | 值 （亿美元） | 世界排名 |
|---|---|---|
| 2015 | 1.2 | 151 |
| 2014 | 2.4 | 142 |
| 2013 | 2 | 137 |
| 2012 | 2.8 | 140 |
| 2011 | 2.5 | 137 |
| 2010 | 2 | 134 |
| 2009 | 1.6 | 128 |
| 2008 | 1.8 | 143 |
| 2007 | 1.5 | 145 |
| 2006 | 1 | 150 |
| 2005 | 0.8 | 143 |
| 2004 | 0.3 | 153 |
| 2003 | 0.3 | 151 |
| 2002 | 0.4 | 134 |
| 2001 | 0.6 | 126 |
| 2000 | 0.7 | 119 |
| 1999 | 0.5 | 129 |
| 1998 | 0.4 | 131 |
| 1997 | 0.5 | 125 |
| 1996 | 0.6 | 110 |
| 1995 | 0.7 | 95 |
| 1994 | 1.1 | 76 |
| 1993 | 0.7 | 86 |
| 1992 | 1.5 | 52 |
| 1991 | 0.1 | 102 |
| 1990 | 0.1 | 107 |
| 1989 | 0 | 134 |
| 1988 | 0 | 107 |
| 1987 | 0 | 104 |
| 1986 | -.1 | 129 |