While much of the current media coverage about the future of cars focuses on the adoption of battery-electric vehicles, lesser known (but probably just as important) is Porsche's efforts to make a carbon-negative "e-fuel." If successfully implemented, the current fleet of internal combustion engine cars around the world could remain in operation while reducing carbon emissions. It would also allow the gas station infrastructure to remain intact. However, e-fuels are currently rather expensive and require a large amount of non-green electricity to make.

As can be seen in this chart, U.S. domestic demand for gasoline was 127.71 billion gallons in 2020. For the purpose of this question, 25 billion gallons of e-fuels purchased in America in any given year would constitute widespread adoption of e-fuels.