| 时间 | 值 （亿美元） | 世界排名 |
|---|---|---|
| 2015 | 18.8 | 70 |
| 2014 | 18 | 75 |
| 2013 | 21.7 | 60 |
| 2012 | 26.8 | 69 |
| 2011 | 17.6 | 74 |
| 2010 | 14.4 | 77 |
| 2009 | 11.8 | 82 |
| 2008 | 17.5 | 83 |
| 2007 | 4.2 | 120 |
| 2006 | 7.5 | 86 |
| 2005 | -.1 | 186 |
| 2004 | 0.3 | 155 |
| 2003 | 1.2 | 119 |
| 2002 | 0.6 | 126 |
| 2001 | 1 | 105 |
| 2000 | -.4 | 178 |
| 1999 | 0 | 155 |
| 1998 | 0 | 174 |
| 1997 | 0.1 | 158 |
| 1996 | 0 | 173 |
| 1995 | 0 | 161 |
| 1994 | 0 | 155 |
| 1993 | 0.2 | 111 |
| 1992 | 0 | 150 |
| 1991 | 0 | 118 |
| 1990 | 0.3 | 83 |
| 1989 | 0.1 | 100 |
| 1988 | 0 | 118 |
| 1987 | 0 | 118 |
| 1986 | 0 | 113 |