Abstract: An improved ink storage system for ink cartridges which allows operation in a rapid and continuous manner while avoiding deprimes. A flexible, resilient ink bladder is provided which consists of an elongate reservoir that is closed at the bottom and open at the top with a tubular side wall therebetween. The bladder is supplied with ink, and a negative pressure is maintained therein. Due to the negative pressure, the side wall collapses inwardly upon ink delivery. To ensure that the wall collapses properly, the bladder is designed so the side wall thickness varies, with some portions of the wall being thinner than others. As a result, the thinner portions collapse inwardly toward the thicker portions during ink delivery. This prevents undesired increases in back-pressure within the bladder, thereby eliminating ink cartridge deprimes.