Marvel Mystery Oil(R) lubricates the entire fuel system-fuel pumps, fuel injectors or carburetors and the top portion of the cylinders. These are areas, that by design, motor oil does not reach. Using Marvel Mystery Oil in your fuel extends the life of these vital components by providing them with lubrication that fuel alone does not provide.Marvel reduces and prevents varnish and gum build-up, two key contributors to robbing engine performance. When you shut off your engine, a miniscule drop of fuel is left at the tip of the fuel injectors or carburetor jets. This miniscule drop off of fuel then solidifies into a varnish type residue. Over time, the accumulated varnish blocks the openings of the injectors or jets, contributing to lower performance and fuel economy and shorter life of these components.