 Most extremely preterm babies require supplemental oxygen for several weeks or even months after birth. The goal of oxygen therapy is to achieve adequate oxygen delivery to the tissues without causing oxygen toxicity and oxidative stress. At present, this goal is elusive in very immature infants. Although it is standard practice in modern neonatal intensive care units to monitor arterial oxygen saturations via pulse oximetry, there is insufficient evidence to guide the choice of the upper and lower alarm limits. A rigorous trial with long-term follow up is urgently needed and long overdue to determine whether oxygen exposure can be reduced safely in extremely preterm infants without increasing the risk of hypoxic death or disability. 