Like all medical therapies, we have learned that treatment with oxygen comes at a cost. The medical literature is replete with the detriments of hyperoxia in the management of myocardial infarction, acute stroke, cardiac arrest and septic shock. What is the optimal oxygenation target for critically ill patients requiring mechanical ventilation? Three landmark trials can guide us: Oxygen-ICU, ICU-ROX and LOCO₂. The end to the oxygenation fairytale remains to be told, but perhaps Goldilocks is “just right.”