An aspirator/nebulizer for use in inhalation therapy has dual oxygen nozzles extending into a cylindrical chamber into which air can be aspirated in a controlled manner via closable air holes. A 50 psig oxygen source can be diluted to atmospheric air to yield an oxygen/air mixture comprising less than 30% oxygen at the conventional patient flow rates of 30-60 liters per minute. The dual oxygen nozzles also allow pure oxygen to be delivered at rates of at least 40 liters per minute when such high flow rates of relatively pure oxygen are needed for short term therapy.