| 时间 | 值 （亿美元） | 世界排名 |
|---|---|---|
| 2016 | 29.1 | 84 |
| 2015 | 30 | 98 |
| 2014 | 28.7 | 98 |
| 2013 | 27.6 | 102 |
| 2012 | 26.7 | 102 |
| 2011 | 22 | 106 |
| 2010 | 20.9 | 112 |
| 2009 | 18.7 | 105 |
| 2008 | 16.4 | 110 |
| 2007 | 15.9 | 109 |
| 2006 | 15.4 | 106 |
| 2005 | 14.8 | 100 |
| 2004 | 13.3 | 102 |
| 2003 | 12.5 | 104 |
| 2002 | 12.8 | 101 |
| 2001 | 13.2 | 99 |
| 2000 | 14.5 | 96 |
| 1999 | 14.9 | 91 |
| 1998 | 15 | 91 |
| 1997 | 14.8 | 91 |
| 1996 | 15.1 | 91 |
| 1995 | 14.7 | 90 |
| 1994 | 14.6 | 85 |
| 1993 | 14.4 | 84 |
| 1992 | 13.5 | 83 |
| 1991 | 12.6 | 82 |