Electricity generation accounts for close to 40% of the U.S. CO2 emissions from fossil fuel burning, making it the economic sector with the largest source of CO2. Since the late 1990s, the Environmental Protection Agency Clean Air Markets Division (EPA CAMD) has kept a repository of hourly CO2 emission data for most power plants in the conterminous United States. In this study, the CAMD CO2 data are used to derive a high spatiotemporal resolution CO2 emissions inventory for the electricity generation sector (inventory available on request). Data from 1998 to 2006 have been processed. This unique inventory can be used to improve the understanding of the carbon cycle at fine temporal and spatial scales. The CAMD data set provides the first quantitative estimates of the diurnal and seasonal cycles of the emissions as well as the year to year variability. Emissions peak in the summertime owing to the widespread use of air conditioning. Summertime emissions are in fact highly correlated with the daily average temperature. In conjunction with the EPA Emissions and Generation Resource Integrated Database (eGRID), we have derived high-resolution maps of CO2 emissions by fossil fuel burned (coal, gas, oil) for the year 2004. The CAMD data set also reflects regional anomalies in power generation such as the August 2003 blackout in the northeastern United States and the 2000–2001 increase in production in California. We recommend that all sectors of the economy report similar high-resolution CO2 emissions because of their great usefulness both for carbon cycle science and for greenhouse gases emissions mitigation and regulation.