A specified concentration of oxygen in a medical gas delivered to a patient by a gas delivery system can be achieved through the use of pulse width modulation control of the flows of one or more component medical gases. The flow of component medical gases can be controlled to improve the resolution and concentration range of medical gas delivered at low flow rates. A first flow of a first medical gas is provided and a second flow of a second medical gas is introduced to achieve a desired average medical gas concentration. When the second flow of the second medical gas is introduced, the first flow of the first medical gas is reduced to maintain a desired total medical gas flow rate.
