Abstract: The apparatus includes magnetic means diametrically opposed at opposite sides of a fuel line conveying hydrocarbon fuel such as gasoline, diesel fuel or the like to the fuel/air mixture means of an internal-combustion engine. The treatment means includes a splitter section for subjecting the fuel to magnetic influence in a first stage or section and subsequently to an expander section including several magnets and collectors through which the fuel line extends coaxially, there being a final direct magnetic exposure contact of the fuel in the expander section.