A degassing system for a hydrocarbon dispenser including a hydrocarbon circulating pump (12). The system includes a degassing assembly (16) having an inlet connected to the outlet of the pump, a degassed hydrocarbon outlet (90), a takeoff outlet (20) for taking off the hydrocarbon/gas mixture, a degassing vessel (24), and a duct (38, 60") for connecting the takeoff outlet to the degassing vessel. The end of the duct which opens out into the degassing vessel has an adjustable effective flow section. The system also includes a valve arrangement (110, 118) for modifying the effective flow section as a function of the gas content of the hydrocarbon.