| 时间 | 值 （亿美元） | 世界排名 |
|---|---|---|
| 2015 | 33.2 | 54 |
| 2014 | 47.8 | 48 |
| 2013 | 51.3 | 40 |
| 2012 | 34 | 55 |
| 2011 | 20.8 | 70 |
| 2010 | 14 | 79 |
| 2009 | 16 | 72 |
| 2008 | 18.6 | 81 |
| 2007 | 9.7 | 93 |
| 2006 | 3.8 | 109 |
| 2005 | 5.2 | 94 |
| 2004 | 3 | 102 |
| 2003 | 10 | 59 |
| 2002 | 0 | 184 |
| 2001 | -.1 | 176 |
| 2000 | 0 | 170 |
| 1999 | -.1 | 175 |
| 1998 | 0.1 | 159 |
| 1997 | 0 | 167 |
| 1996 | 0 | 175 |
| 1995 | 0 | 151 |
| 1994 | 0 | 162 |
| 1993 | 0 | 150 |
| 1992 | 0.1 | 117 |
| 1991 | 0 | 144 |
| 1990 | 0 | 130 |
| 1989 | 0 | 114 |
| 1988 | 0 | 126 |
| 1987 | 0.1 | 83 |
| 1986 | 0 | 102 |