Supplementary oxygen is widely used in critically unwell patients; however, the optimal regime of oxygen therapy is a topic of ongoing debate. Although hypoxemia is dangerous, in vitro evidence suggests that exposing alveolar epithelium to supranormal oxygen concentration causes free radical formation (1). Clinically, hyperoxia (defined as a PaO2 value greater than the normal range for a patient’s age when breathing air [2]) can lead to absorption atelectasis, central nervous system toxicity, reduced cardiac output, and systemic vasoconstriction, all of which could compound critical illness. To mitigate this, the safety of conservative oxygen therapy has been investigated in critically ill patients, and several studies have demonstrated noninferiority of conservative oxygen therapy (3–5), whereas a meta-analysis found that this strategy conferred a mortality benefit (6). The following recent articles (Table 1) assess the effect of conservative versus liberal oxygen treatment on patient outcomes in the critical care environment. The importance of this literature is emphasized by ongoing challenges associated with an expanding number of critically ill patients and increased demand on healthcare resources, in particular oxygen reserves.