is an oily, viscous contaminant that may form due to oxidation during storage. Gum formation in gasoline can cause serious fuel system problems, such as carburetor malfunctioning and intake valve sticking. The amount of gum in motor gasoline, aviation gasoline, and aircraft turbine fuel can be determined by evaporating a measured sample by means of air or steam flow at controlled temperature, and weighing the residue, as described in test method ASTM-D-381.