Absolute minimum energy penalties are calculated and reported for 5 different CO2 emission reduction technologies: carbon capture and sequestration from point sources, carbon capture and sequestration from air, carbon capture and utilization as structural materials, steam methane reforming with carbon capture and sequestration, and methane pyrolysis. The absolute minimum energy penalties are calculated from minimum work calculations based on classical thermodynamics. These energy penalties represent the thermodynamically defined minimum energetic costs of each process. Real processes have higher energetic costs, as well as additional operating and capital costs. These calculations place each of the technologies in context with respect to each other and to the existing energy infrastructure by specifying lower bounds on the costs of pursuing these technologies on an equivalent energy basis. (C) 2019 Published by Elsevier Ltd.