On this site you will find on eBay hundreds of sellers of kits designed to improve gas mileage by using hydrogen converters. We are not associated with any sellers and we have no information as to whether they work as well as they are supposed to, or even if they work at all, so its definitely a case of "buyer beware" . So until such time as the major makers mass-produce cars run entirely on hydrogen, take a look at short-term alternatives.