Abstract The United States (U.S.) electric power sector historically comprises the largest portion of greenhouse gas (GHG) emissions from the world's second-largest GHG emitter. Consequently, carbon accounting methods employed for this economic sector play an important role in ensuring the accuracy of carbon accounts globally. For the U.S., the diverse purposes and methods of eight federal data products yield eight different estimates of U.S. electric-sector carbon dioxide emissions. Prior studies neither fully characterized these differences nor evaluated the data products' ability to capture changes in carbon dioxide emissions from certain now-minor sources of electricity that are projected to increase as the grid modernizes. Here we explore how shifts in electricity sources might impact current carbon accounting methods. We show that if no changes are made, four of the six data products could exclude (via omission or attribution) 1.1%–3.3% of carbon dioxide emissions from U.S. electricity generation in 2040. Maintaining comprehensive tracking of electric-sector emissions through the suggestions made herein can help enable efficient allocation of mitigation resources.