| 时间 | 值 （亿美元） | 世界排名 |
|---|---|---|
| 2012 | 0.4 | 91 |
| 2011 | 0.4 | 96 |
| 2010 | 0.5 | 88 |
| 2009 | 0.6 | 86 |
| 2006 | 6.7 | 75 |
| 2005 | 2.5 | 76 |
| 2004 | 4.5 | 68 |
| 2003 | 1.5 | 75 |
| 2002 | 1.1 | 78 |
| 2001 | 3.9 | 59 |
| 2000 | 6.9 | 54 |
| 1999 | 7.7 | 52 |
| 1998 | 15.3 | 48 |
| 1997 | 38.6 | 48 |
| 1996 | 12.8 | 50 |
| 1995 | 5.1 | 51 |
| 1994 | 9.4 | 45 |
| 1993 | 18.7 | 40 |
| 1992 | 26.3 | 36 |
| 1991 | 32.4 | 30 |
| 1990 | 22.3 | 30 |
| 1989 | 0.9 | 39 |
| 1988 | 2.2 | 35 |