A replaceable ink cartridge, usable with a bubble jet printer, includes a container having front, back, top bottom and side walls, the container being divided internally into a first chamber and a second chamber having a common partition extending downward perpendicularly toward the bottom wall to provide an opening between the chambers formed by the partition proximate to the bottom wall. The first chamber contains a reservoir of liquid ink and is generally sealed from ambient air except through the opening, and the second chamber has an air vent for admitting ambient air into the second chamber and an ink supply outlet in the front wall. The second chamber contains a sponge-like material for retaining ink, at least one groove in the second chamber side of the partition extending from the opening and terminating at a point partly up the partition to form an air flow passage from the second chamber to the first chamber, the sponge-like material being positioned in the second chamber to permit flow of air from the air vent to the groove when the level of retained ink in the sponge-like material is proximate to the point where the groove terminates. The container is removably mountable in a printer mounting with the bottom wall facing downward and the ink supply outlet facing an ink jet print head so that the ink supply outlet is connectable to an ink port of the ink jet print head.