Abstract: In anesthesia apparatus, an integrated oxygen ratio controller is provided for supplying oxygen and an anesthesia gas through respective flow control valves to a patient breathing circuit. The integrated oxygen ratio controller includes differential pressure sensing means and anesthesia gas flow control means. The differential pressure sensing means includes a rolling diaphragm forming a portion of one wall of a chamber responsive to the pressure in the oxygen pipeline and another rolling diaphragm forming a portion of one wall of another chamber responsive to the pressure in the anesthesia gas pipeline. The anesthesia gas flow control means controls the flow of gas to the anesthesia gas pipeline. The rolling diaphragms are opposed to each other and are coupled together by a displaceable means. The displaceable means is also coupled to the anesthesia gas flow control means to control the flow of anesthesia gas therethrough in response to the differential pressure existing between the pipelines.