Apparatus and method for forming a self-standing skirt on the pressure bottom of a blow-molded carbonated beverage container. The preform is formed with an annular depending skirt, and the skirt is stretched with a stretch mechanism which engages all but a lower portion of the preform, so that during the stretching of the preform concurrently with the blowing of the preform in a bottle mold, the lower portion folds inwardly to form a bottom ledge on the stretched skirt. The mold is provided with a centering mechanism for assuring the centering of the preform within the mold cavity to assure that the preform skirt receives the skirt stretching mechanism.