Systems and methods for infusion of fluids using stored potential energy and a variable flow resistor (60) . In one aspect of the present disclosure, there is provided an infusion device (10) that includes a plunger (24) situated within a vessel (11) so as to define a chamber (26) within which a volume of fluid (40) can be accommodated between a downstream surface of the plunger and the vessel. The infusion device further includes an outflow path (13) through which the fluid in the chamber can be dispensed upon displacement of the plunger by a force acting thereon. A variable flow resistor is situated within the outflow path and is configured to allow a substantially constant fluid flow rate from the vessel to be maintained as the force acting on the plunger decreases.