content: Not really, MUCH is a big stretch.  Gas has to obey conservation of mass.  If a bunch of gasoline is burnt you can't reduce co2 or no output.  It just doesn't work with the chemistry.  The thing that has been helping us is lighter cars with smaller engines that burn fuel more completely.  These are things that apply to all cars. The internal combustion fossil fuel engine has been approaching an assymtote for the past decade, but in terms of emission and efficencies.