Evaporative emissions from automotive fuel systems have been recognized as one contributor to photochemical smog and ozone pollution, and so are subject to increasingly stringent regulation. An attractive strategy is to limit the amount of fuel vapor generated in the fuel system, thus easing the burden on the vehicle systems needed to store and eliminate vapor. High fuel tank temperature is a major contributor to vapor generation. Many efforts to reduce the temperature inside a fuel tank have been attempted such as mechanical or electrical returnless fuel systems. Even though these systems reduce vapor generation by about 80% compared to conventional return systems, further improvements may be possible. One way to identify possible improvements is to separately examine the vapor generation of fuel system components, such as fuel pumps, pressure regulators, and jet pumps. Most of these components have an orifice or a narrow flow path which generates low pressure. If this low pressure is below fuel vapor pressure, then vapor bubbles are formed in the liquid fuel. In this paper, the amount of vapor generated by the fuel system components was separately measured. Several different geometrical modifications of each component were tested to find any effects on the vapor generation.