| 年份 | 分类 | 数值 |
| 2007 | United States : coal percent | 8.95 |
| 2008 | United States : coal percent | 8.94 |
| 2009 | United States : coal percent | 8.81 |
| 2010 | United States : coal percent | 8.81 |
| 2011 | United States : coal percent | 8.76 |
| 2012 | United States : coal percent | 8.74 |
| 2013 | United States : coal percent | 8.63 |
| 2014 | United States : coal percent | 8.56 |