Iatrogenic hyperoxaemia is common on Critical Care Units (CCUs) throughout the world and high blood oxygen levels have been associated with adverse outcomes including increased mortality. We have commenced a pilot quality implementation study to analyse the views of Critical Care staff regarding oxygen therapy and to change practice to ensure that all patients in the Critical Care Unit have a prescribed target oxygen saturation range. 33 CCU staff responded to an online questionnaire (16 doctors, 7 nurses, 9 physiotherapists, 1 ACCP). 76% thought that slightly too much oxygen was used on the unit but only 53% favoured a formal prescription for oxygen for all patients. For ventilated patients not at risk of hypercapnia, 83% would favour a target range of 94%–98% and 10% would opt for a target range of 90%–94%. For patients at risk of hypercapnia, all respondents favoured a target range of 88%–92%. A baseline audit of practice on the unit studied 54 patients (28 on ventilators) over one month prior to the implementation of a programme of change. 85% of audited patients (46 of 54) had a formal oxygen prescription with target range. Forty patients had target range 94%–98% and six patients had target range 88%–92%, all prescriptions were judged to be appropriate. The mean PaO₂ on blood gas samples was 13.1 kPa compared with 15.1 kPa in 2005 and 14.9 kPa in 2010. Mean PaCO₂ was 5.3 kPa. The mean SpO₂ (pulse oximetry) was 96.8% [median 97%, range 91%–100%]. 82% of SpO₂ values were within the target range but four of six patients with target range 88%–92% were at least 2% above this range. Attitudes and practice in our Critical Care Unit have changed in the past decade and hyperoxaemia is less common now. However, practice still lags behind the declared ambition of our Critical Care colleagues to maintain normoxaemia for most patients. We have instituted changes to CCU practice in May-June 2017. These changes will inform the design of a systematic randomised cluster implementation study using a step-wedge design to implement current best practice in a wide range of Critical Care units.