The electricity data is collected and prepared for release by the Office of Electricity, Renewables and Uranium Statistics, Office of Energy Statistics, U.S. Energy Information Administration (EIA), U.S. Department of Energy. The data are compiled from the following EIA survey sources (including predecessor forms): Form EIA-826,"Monthly Electric Utility Sales and Revenues with State Distributions Report," Form EIA-923, "Power Plant Operations Report," EIA-860, "Annual Electric Generator Report," and the EIA-861, "Annual Electric Power Industry 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 2011 should be final by the fall of 2012).
For complete documentation on EIA monthly electric data collection and estimation, see the Technical Notes (Appendix C) to the Electric Power Monthly.