Abstract: The invention is embodied in a pressurized ink supply system for a three color ink jet printer. In order to provide a relatively large ink supply, three stationary primary ink reservoirs, formed as three long tubular sacks of flexible plastic film, contained in a pressurized disposable cartridge, are connected through flexible plastic umbilical tubes, and three solenoid-operated valves, to three secondary ink reservoirs mounted on the movable carriage of the print head. Automatic ink replenishment and an out-of-ink alarm are controlled entirely from the secondary ink reservoirs.The ink level in each secondary reservoir is maintained within close limits without attention from the operator. When the primary reservoir runs out of ink, as indicated by failure of the secondary reservoir to fill within a specified time period, an alarm alerts the operator to remove and replace the ink cartridge.