On September 20, 2013, the U.S. Environmental Protection Agency (EPA) released a revised proposed rule regulating carbon dioxide (CO2) emissions from electric generating units (EGUs) under the Clean Air Act’s New Source Performance Standards (NSPS). This proposal will have significant and immediate impacts because NSPS regulations are effective for new sources as soon as the proposed rule is published in the Federal Register. The proposed NSPS standard replaces EPA’s April 13, 2012, proposal, which EPA will rescind at the same time it publishes the revised proposal. While the revised proposal includes a number of significant changes from the earlier proposal—notably, separate standards for coal- and natural gas-fired EGUs—it maintains strict emissions limits for coal-fired EGUs that will require carbon capture and storage (CCS) for any new facility. The proposed standard applies only to newly constructed sources that have not commenced construction at the time of publication in the Federal Register. Modified and reconstructed sources, as well as existing sources are expected to be addressed in separate rulemakings in 2014.