Units = number of employees. The U.S. coal data is collected and prepared for release by the Office of Oil, Gas, and Coal Supply Statistics, U.S. Energy Information Administration (EIA), U.S. Department of Energy. The data are compiled from the following EIA survey source: Form EIA-7A, 'Coal Production and Preparation Report' and the U.S. Department of Labor, Mine Safety and Health Administration, Form 7000-2, 'Quarterly Mine Employment and Coal Production Report.' Note that data for the most current time periods typically represent preliminary estimates based on samples collected by the surveys. After the end of a calendar year the estimates are replaced by actual values from a final data collection, except in the case of missing values. Missing values (non-response) is typically minimal. Normally all data are final by the fall following the data collection year (e.g., data for 2012 should be final by the fall of 2013). For more information concerning EIA's annual coal data collection and estimation, see the individual footnotes contained in the Annual Coal Report (http://www.eia.gov/coal/annual/).