Objectives:To investigate attitudes and practices regarding oxygen therapy in intensive care units (ICUs) and to devise quantitative descriptive indices.Setting:Canadian university-affiliated adult ICUs.Participants:Fifty-two medical directors of ICUs in 48 institutions.Intervention:Structured postal questionnaire returned by 48 participants.Measurements and Main Results:Attitudes, beliefs, and stated practices relating to oxygen use in ICUs were determined. Novel descriptors S-50min(minutes of oxygen saturation [SaO2] acceptable to >50% of respondents), F-50max(maximum FIO2above which <50% of respondents would increase FIO2), and F-50min(minimum FIO2below which <50% of respondents would decrease FIO2) were determined. All respondents believed that oxygen toxicity was a concern. Twenty-nine percent of respondents indicated that they did not always assess tissue oxygenation in critical cases. A stepwise reduction in acceptance of progressive desaturation and increasing duration of hypoxemia was found. Presented with a stable patient with SaO2of 98%, the maximum level of FIO2above which respondents stated that they would not increase the FIO2was 0.41 ± 0.17 (mean ± SD). For stable patients with SaO2of 85%, the minimum FIO2below which respondents would not reduce FIO2was 0.59 ± 0.23 (mean ± SD). F-50maxwas 0.8 vs. 0.5 for SaO2of 80%-85% vs. 85%-90%, respectively; F-50minwas 0.6 vs. 0.21 for SaO2of 90%-95% vs. 95%-100%, respectively.Conclusions:Considerable variation exists in the attitudes, beliefs, and stated practices relating to the management of oxygen therapy in the ICU. These data are amenable to quantitative description and illustrate the necessity for documentation of actual practice and development of support systems for decision-making in this and similar areas.