The present invention provides improved anesthesia delivery systems that consistently and reliably deliver anesthesia gas to multiple gas outlets. The systems are particularly useful for anesthetizing multiple mammals and living specimens to be imaged by a low-light level imaging system. The anesthesia delivery systems are suitable for use with conventional oxygen sources, and convert the high pressures associated with a conventional oxygen source to lower pressures suitable for use with small mammals and suitable for combination with an anesthesia gas at low flow rates. The systems include an anesthesia gas source that combines anesthesia gas with the oxygen. The combination of anesthesia gas and oxygen is supplied to one or more multiple outlets.