Abstract: A method of filling a pressurized package, and apparatus therefor, is described in which a unitary valve body is aligned with a container neck, fluid under pressure is introduced through the neck and around the valve and then the valve is forced into the neck to seal the container, the valve having a body portion preformed to engage in a neck portion with interference, including rib and groove engagement, and the neck portion having a smallest diameter to depth ratio no greater than 5:1, and the valve body portion being long enough to extend through the neck to bulge into the container with the internal pressure of the container acting inside the valve to force the valve body portion radially against the neck portion.