| 年份 | 分类 | 数值 |
| 2007 | United States : coal percent | 0.97 |
| 2008 | United States : coal percent | 1.01 |
| 2009 | United States : coal percent | 1.16 |
| 2010 | United States : coal percent | 1.19 |
| 2011 | United States : coal percent | 1.25 |
| 2012 | United States : coal percent | 1.29 |
| 2013 | United States : coal percent | 1.32 |
| 2014 | United States : coal percent | 1.29 |