| 时间 | 值 （亿美元） | 世界排名 |
|---|---|---|
| 2012 | 1.2 | 81 |
| 2011 | 1.2 | 82 |
| 2010 | 1.8 | 77 |
| 2009 | 2.7 | 78 |
| 2008 | 16.6 | 64 |
| 2007 | 2.3 | 83 |
| 2006 | 2.3 | 82 |
| 2005 | 2.4 | 77 |
| 2004 | 3.7 | 71 |
| 2003 | 2.6 | 67 |
| 2002 | 2.7 | 64 |
| 2001 | 4.3 | 58 |
| 2000 | 12.1 | 49 |
| 1999 | 10.4 | 50 |
| 1998 | 11.7 | 52 |
| 1997 | 5.6 | 55 |
| 1996 | 5.3 | 53 |
| 1995 | 2.1 | 60 |
| 1994 | 2.7 | 53 |
| 1993 | 11 | 44 |
| 1992 | 1.2 | 47 |
| 1991 | 1.4 | 44 |
| 1990 | 0.9 | 40 |
| 1989 | 1.1 | 38 |
| 1988 | 2.6 | 34 |