UK-ROX, the largest ever clinical trial of oxygen use in UK intensive care units (ICUs), has shown that reducing supplementary oxygen does not deliver any clear and obvious health benefits or harm a patient's chances of survival. Each year, around 184,000 patients are admitted to ICUs, but there is insufficient evidence to guide the use of oxygen, with the possibility that administering too much - or too little - may not deliver the intended benefits and actually end up causing patients additional harm. UK-ROX, led by the University of Plymouth and the Intensive Care National Audit & Research Centre, set out to fill that evidence gap and the results have been presented to delegates at the Critical Care Reviews Meeting 2025 in Belfast this morning, and published in the JAMA journal.