An ink cartridge suitable for regulating a hydrostatic pressure of ink supplied to an inkjet printhead is provided. The cartridge comprises an ink chamber having an ink outlet for fluid communication with the printhead via an ink line; an air inlet open to atmosphere; a bubble outlet for bubbling air bubbles into the chamber, each air bubble comprising an air cavity trapped inside a film or a body of ink; and an air channel connecting the air inlet and the bubble outlet. The bubble outlet is dimensioned to control a Laplace pressure of air bubbles drawn into the chamber as result of supplying ink to the printhead, thereby regulating a hydrostatic pressure of the ink.