A Method of Processing a Container and Base Cup Structure For Removal of Vacuum Pressure A plastic container (10) has a wall extending to a lower portion including a pressure panel (20). The panel (20) is transversely oriented and can move from a downwardly inclined position providing a geometrically unstable configuration to an upwardly inclined position providing a geometrically stable configuration to control pressure change in the container. This movement may be provided by suitable actuating means such as rod (22). In the unstable configuration a base cup 50 or any other suitable holder can support the container and enable it to be conveyed in a container handling or processing system.