| 时间 | 值 （亿美元） | 世界排名 |
|---|---|---|
| 2015 | 19.6 | 68 |
| 2014 | 20.4 | 68 |
| 2013 | 20.9 | 64 |
| 2012 | 18 | 73 |
| 2011 | 12.3 | 88 |
| 2010 | 18.1 | 68 |
| 2009 | 9.5 | 87 |
| 2008 | 13.8 | 91 |
| 2007 | 5.8 | 115 |
| 2006 | 4 | 108 |
| 2005 | 9.4 | 79 |
| 2004 | 4.4 | 88 |
| 2003 | 3.2 | 91 |
| 2002 | 4 | 75 |
| 2001 | 5.5 | 65 |
| 2000 | 4.6 | 62 |
| 1999 | 5.2 | 63 |
| 1998 | 1.7 | 98 |
| 1997 | 1.6 | 95 |
| 1996 | 1.5 | 80 |
| 1995 | 1.2 | 79 |
| 1994 | 0.5 | 96 |
| 1993 | 0.2 | 109 |
| 1992 | 0.1 | 110 |
| 1991 | 0 | 137 |
| 1990 | 0 | 136 |
| 1989 | 0.1 | 103 |
| 1988 | 0 | 104 |
| 1987 | 0 | 130 |
| 1986 | -.1 | 125 |