Marvel Mystery Lubricating Oil is safe for catalytic converters and oxygen sensors. Added to gas it cleans and lubricates fuel injectors and carburetors, improves gasoline mileage, extends spark plug life, reduces and prevents varnish and gum build-up. Added to oil it prevents valve sticking and clatter, fortifies properties of engine oil, prevents breakdown caused by extreme temperatures, reduces and prevents acid and sludge formation and promotes easier cold weather starts.