A fluid-responsive vent control valve for an automobile fuel tank in which a liquid level responsive float controls a flexible, ribbon type valve member to peel it on and off a valve seat to open and close the valve. In one embodiment the float and outlet structure are offset. In an alternate embodiment the float and vent outlet are coaxial, and the ribbon valve is attached between the float and the valve body with a vent closure portion aligned with the outlet and a hinge portion offset from the outlet and connected to the float to provide opening and closing force to the ribbon valve. The outlet is preferably circular, and further includes a roundoff notch which cannot be closed by the pressure differential across the ribbon valve, but requires a final closing movement by the float and closure assist structure to fully close the valve.