| 时间 | 值 （亿美元） | 世界排名 |
|---|---|---|
| 2015 | 3.1 | 178 |
| 2014 | 3.1 | 183 |
| 2013 | 2.8 | 187 |
| 2012 | 2.8 | 187 |
| 2011 | 2.5 | 190 |
| 2010 | 2.3 | 189 |
| 2009 | 2.2 | 189 |
| 2008 | 2.6 | 187 |
| 2007 | 2.5 | 188 |
| 2006 | 2.6 | 187 |
| 2005 | 2.5 | 186 |
| 2004 | 2.4 | 187 |
| 2003 | 2.1 | 186 |
| 2002 | 2.2 | 185 |
| 2001 | 2.2 | 180 |
| 2000 | 2.4 | 179 |
| 1999 | 1.8 | 178 |
| 1998 | 1.7 | 178 |
| 1997 | 1.7 | 178 |
| 1996 | 1.7 | 177 |
| 1995 | 1.4 | 176 |
| 1994 | 1.2 | 171 |
| 1993 | 1 | 165 |
| 1992 | 0.9 | 164 |
| 1991 | 1 | 161 |