P OSTOPERATIVE pulmonary complications are common and affect morbidity and mortality in patients undergoing major surgery. 1 Intraoperative ventilation strategies for lung protection include low tidal volume, positive end-expiratory pressure (PEEP), and recruitment maneuvers. These strategies appear to improve clinical outcomes in patients undergoing major abdominal surgery. 2 However, the strategies do not consider supplemental oxygen, which is an essential component of ventilator management. Supplemental oxygen administration during mechanical ventilation is important for preventing or correcting hypoxemia, both in the intensive care unit and in the operation theater. Several observational studies of intensive care unit patients receiving mechanical ventilation found that conventional oxygen therapy was liberally administered, and this could potentially induce hyperoxemia, 3-6 which is a potentially injurious condition. High oxygen levels can enhance reactive oxygen species formation and oxidative stress, induce peripheral vasoconstriction, and decrease cardiac output. 7,8 Moreover, adverse clinical outcomes What We Already Know about This Topic • Despite the potentially harmful effects of oxygen overexposure, supplemental oxygen therapy is commonly prescribed in several clinical conditions. However, little is known about current oxygen administration practices during general anesthesia. What This Article Tells Us That Is New • In this multicenter, cross-sectional study of 1,498 patients at 43 hospitals, potentially preventable hyperoxemia and substantial oxygen exposure were common during general anesthesia, especially in patients receiving one-lung ventilation.