Abstract: A vapor pressure control system for controlling the vapor pressure in a fuel storage tank is provided which comprises a cooling chamber for cooling the fuel vapor, wherein the temperature of the cooling chamber is maintained at a point slightly above the freezing point of water. Vapor intake and return lines provide for communication of the fuel vapor between the tank and the cooling chamber. A fan interposed in the intake line causes the circulation of the fuel vapor between the tank and the cooling chamber. The fan is operated by a pressure sensitive switch which causes the fan to run when the difference between the ambient air pressure and tank vapor pressure falls below a certain minimum level, and which causes the fan to stop when the difference between the ambient air pressure and tank vapor pressure rises above a certain, maximum level. The fan is shut off by a temperature sensitive switch when the ambient temperature approaches the freezing point of water.