Abstract: When a tank filler tube cap is closed, several flow paths having solenoid-operated valves are selectively operated by an engine management computer to control pressurizing of a bladder disposed in a fuel tank and of surrounding fuel vapor space not occupied by the bladder to attenuate fuel vapor generation. Venting of the bladder to atmosphere and of the vapor headspace to a canister are also controlled. The control further regulates the pressure in the bladder relative to that in the vapor headspace. On-board testing for leakage can be automatically accomplished for ascertaining compliance with relevant regulations. When the tank is to be re-fueled, a signal is sent to the computer.