| 时间 | 值 （亿美元） | 世界排名 |
|---|---|---|
| 2015 | 3 | 129 |
| 2014 | 3.3 | 135 |
| 2013 | 3.6 | 124 |
| 2012 | 2.3 | 144 |
| 2011 | 4.2 | 128 |
| 2010 | 2.2 | 132 |
| 2009 | 1.6 | 130 |
| 2008 | 1.8 | 141 |
| 2007 | 1.3 | 151 |
| 2006 | 0.6 | 157 |
| 2005 | 0.5 | 147 |
| 2004 | 0.5 | 148 |
| 2003 | 0.3 | 147 |
| 2002 | 0.2 | 145 |
| 2001 | 0.2 | 140 |
| 2000 | 0.2 | 144 |
| 1999 | 0.1 | 146 |
| 1998 | 0.1 | 152 |
| 1997 | 0.1 | 157 |
| 1996 | 0.1 | 149 |
| 1995 | 0.1 | 142 |
| 1994 | 0.1 | 133 |
| 1993 | 0.1 | 135 |
| 1992 | 0.1 | 120 |
| 1991 | 0.1 | 113 |
| 1990 | 0.1 | 115 |
| 1989 | 0 | 105 |
| 1988 | 0 | 114 |
| 1987 | 0.1 | 100 |
| 1986 | 0.1 | 88 |