An ink cartridge for an inkjet printer is provided. The cartridge has an ink storage compartment having opposed wall sections connected by a flexible wall arrangement to define a variable ink storage volume, and an ink feed system for supplying ink to a printhead with an array of nozzles. One of the opposed wall sections is displaceable and biased to expand the variable ink storage volume to create a negative pressure in the ink storage compartment for avoiding inadvertent ink leakage from the nozzles.