The transport sector is often seen as the most difficult sector to decarbonize. In recent years, so-called electrofuels have been proposed as one option for reducing emissions. Electrofuels-here defined as fuels made from electricity, water, and carbon dioxide-can potentially help manage variations in electricity production, reduce the need for biofuels in the transportation sector while utilizing current infrastructure, and be of use in sectors where fuel switching is difficult, such as shipping. We investigate the cost-effectiveness of electrofuels from an energy system perspective under a climate mitigation constraint (either 450 or 550 ppm of CO2 in 2100), and we find the following: (i) Electrofuels are unlikely to become cost-effective unless options for storing carbon are very limited; in the most favorable case modeled-an energy system without carbon storage and with the more stringent constraint on carbon dioxide emissions-they provide approximately 30 EJ globally in 2070 or approximately 15% of the energy demand from transport. (ii) The cost of the electrolyzer and increased availability of variable renewables appear not to be key factors in whether electrofuels enter the transport system, in contrast to findings in previous studies.