An ink supply system for an inkjet printer. The ink supply system includes: an upstream ink conduit for connection with an ink inlet of a printhead; a pressure-regulating chamber having an outlet port connected to the upstream ink conduit, the chamber containing ink at a first level below the printhead, wherein a headspace above the first level of ink is open to atmosphere; and a downstream ink conduit for connection with an ink outlet of the printhead, the downstream ink conduit extending above the first level of ink and being open to atmosphere. The downstream ink conduit has a loop section passing below the first level of ink, such that, in a printing configuration, a second level of ink in the loop section is equal to the first level of ink in the chamber.