A pneumatic oxygen conserving device for efficiently dispensing oxygen or other gas used during respiratory therapy such that only the first part of the patient's breath contains the oxygen or other therapeutic gas. A gas delivery device is used which is triggered when the patient begins to inhale. A tail of gas flow is delivered to the patient after the initial inhalation timed period to prevent pulsing of gas delivery to the patient. In this manner gas is only delivered to the patient during the first portion of inhalation preventing gas from being delivered which will only fill the air passageways to the patient's lungs. By efficiently using the oxygen, cylinder bottles of oxygen used when a patient is mobile will last longer and be smaller and easier to transport. By pneumatically delivering the gas to the patient no batteries or electronics are used.