Disclosed is a novel multi-chamber ink-jet print cartridge (pen) that is formed of a main body member divided into three sections, a center section, and two side sections. Cover members are attached to this main body section to define three ink chambers. Each ink chamber contains a synthetic foam member that receives a respective one of three primary colored inks. The main body member is molded to be a single unitary part, so that the only ink-to-ink sealing interface between inks of different colors occurs at the interface between the main body member and the printhead. The main body member is formed to have a center ink pipe that extends upwardly into compressive contact with the foam member in the center chamber, and two side ink pipes that extend outwardly in a direction orthogonal to the center ink pipe into compressive contact with the foam held in the side ink chambers. The disclosed multi-chamber pen thus allows for a narrow pen body with a small printhead, yet also provides for a large volume of ink in each of the three ink chambers, without the need for a separate manifold member and the disadvantageous introduction of additional ink-to-ink interfaces.