A reservoir is provided for a printhead in an ink jet printing machine, the printhead having at least one printhead inlet at a rear face thereof for flow of ink from the reservoir into the printhead. The reservoir comprises a perimeter wall sealably mounted to the rear face of the printhead and defining a chamber in communication with the printhead inlet. The chamber is open at one face and the reservoir includes a resilient flexible membrane attached to the perimeter wall and covering the one face. An inlet is provided in communication with the chamber for passage of ink into the chamber. The resilient flexible membrane has an initial relaxed condition in a first state in which the reservoir is substantially full of ink, and a flexed condition in which the membrane is collapsed into the chamber.