| 时间 | 值 （亿美元） | 世界排名 |
|---|---|---|
| 2015 | 0.3 | 174 |
| 2014 | 0.1 | 180 |
| 2013 | 0.6 | 157 |
| 2012 | 0.6 | 166 |
| 2011 | 0.6 | 165 |
| 2010 | 0.6 | 164 |
| 2009 | 0.3 | 166 |
| 2008 | 0.4 | 173 |
| 2007 | 0.3 | 175 |
| 2006 | 0.4 | 162 |
| 2005 | 0.1 | 165 |
| 2004 | 0.2 | 161 |
| 2003 | 0.2 | 158 |
| 2002 | 0.1 | 153 |
| 2001 | 0.2 | 145 |
| 2000 | 0.2 | 146 |
| 1999 | 0.1 | 145 |
| 1998 | 0.2 | 142 |
| 1997 | 0.3 | 134 |
| 1996 | 0.3 | 119 |
| 1995 | 0.3 | 116 |
| 1994 | 0.3 | 107 |
| 1993 | 0.3 | 106 |
| 1992 | 0.3 | 89 |
| 1991 | 0.3 | 83 |
| 1990 | 0.1 | 98 |
| 1989 | 0.1 | 97 |
| 1988 | 0.1 | 92 |
| 1987 | 0.1 | 84 |
| 1986 | 0 | 101 |