Objective: Hyperoxia is associated with adverse outcome in severe traumatic brain injury (TBI). This study explored differences in patient classification of oxygen exposure by PaO 2 cutoff and cumulative areaunder-the-curve (AUC) analysis. Methods: Retrospective, explorative study including children (<18 years) with accidental severe TBI (2002-2015). Oxygen exposure analysis used three PaO 2 cutoff values and four PaO 2 AUC categories during the first 24 hours of Pediatric Intensive Care Unit (PICU) admission. Results: Seventy-one patients were included (median age 8.9 years [IQR 4.6-12.9]), mortality 18.3% (n = 13). Patient hyperoxia classification differed depending on PaO 2 cutoff vs AUC analysis: 52% vs. 26%, respectively, were classified in the highest hyperoxia category. Eleven patients (17%) classified as 'intermediate oxygen exposure' based on cumulative PaO 2 analysis whereby they did not exceed the 200 mmHg PaO2 cutoff threshold. Patient classification variability was reflected by Pearson correlation coefficient of 0.40 (p-value 0.001). Conclusions: Hyperoxia classification in pediatric severe TBI during the first 24 hours of PICU admission differed depending on PaO 2 cutoff or cumulative AUC analysis. We consider PaO 2 cumulative (AUC) better approximates (patho-)physiological circumstances due to its time-and dose-dependent approach. Prospective studies exploring the association between cumulative PaO 2 , physiological parameters (e.g. ICP, PbtO 2) and outcome are warranted as different patient classifications of oxygen exposure influences how its relationship to outcome is interpreted.