An anesthesia vaporizer system includes a sump chamber, a variable volume reservoir within the sump chamber, and an anesthetic vaporizer. The variable volume reservoir is configured to contain anesthetic agent. A pressurized gas source is connected to the sump chamber and configured to maintain a constant pressure within the sump chamber to compress the variable volume reservoir to force the anesthetic agent through the anesthetic vaporizer, which vaporizes the liquid anesthetic agent for delivery to a patient.