Espite oxygen being one of the most frequently administered substances in the hospital environment, there is little empirical data regarding its use. Review of the literature regarding the clinical assessment of hypoxia and hypoxaemia reveals inconsistency in the definition of terms and raises questions as to the reliability of the clinical indicators currently used to assess the need for supplemental oxygen. Assessment of the need for supplemental oxygen and continued re-evaluation of the patient's oxygen requirements is a nursing responsibility. Physical assessment, in combination with pulse oximetry, is the most common method used by nurses to assess oxygenation status. This paper critically appraises the literature to examine the reliability of clinical indicators of oxygenation used by nurses in acute care settings.