| 时间 | 值 （亿美元） | 世界排名 |
|---|---|---|
| 2016 | 30.6 | 81 |
| 2015 | 32.7 | 94 |
| 2014 | 33.9 | 92 |
| 2013 | 33.3 | 93 |
| 2012 | 32.1 | 92 |
| 2011 | 32 | 92 |
| 2010 | 30.4 | 96 |
| 2009 | 29.3 | 91 |
| 2008 | 27.9 | 90 |
| 2007 | 28.1 | 89 |
| 2006 | 24.3 | 89 |
| 2005 | 21.5 | 92 |
| 2004 | 21.7 | 89 |
| 2003 | 20.9 | 88 |
| 2002 | 21.4 | 87 |
| 2001 | 21.9 | 85 |
| 2000 | 20 | 86 |
| 1999 | 18.6 | 87 |
| 1998 | 18.2 | 87 |
| 1997 | 18.9 | 85 |
| 1996 | 18.6 | 83 |
| 1995 | 18.3 | 84 |
| 1994 | 17.9 | 78 |
| 1993 | 17.5 | 78 |
| 1992 | 16.8 | 74 |
| 1991 | 15.8 | 76 |
| 1990 | 15.8 | 73 |
| 1989 | 15.5 | 63 |