Background: Oxygen therapy is life-saving, but inappropriate administration causes morbidity and mortality. Knowledge gaps among emergency clinicians in resource-limited, high-acuity settings may compromise patient safety. This study aimed to assess the level of knowledge and associated factors regarding oxygen therapy among clinicians at the adult Emergency Department of Tikur Anbessa Specialized Hospital, the largest tertiary referral center in Ethiopia. Methods: We conducted an institution-based cross-sectional study from June to November 2025. A stratified random sample of 108 clinicians (51 residents, 57 nurses) completed a validated, pretested 15-domain self-administered questionnaire. Satisfactory knowledge was defined as a score above or equal to 60 %, based on the modified Bloom's cut-off point. Bivariate and multivariable logistic regression identified independent predictors, with statistical significance established at p <= 0.05. Results:Overall, 60.2% (65/108) achieved satisfactory knowledge. Residents outperformed nurses (70.6% vs 50.9%). In adjusted analysis, prior formal training showed the strongest association with satisfactory knowledge (AOR 37.04, 95% CI 10.16–134.98, p=0.001). Availability of oxygen therapy guidelines in the working area increased odds nearly fivefold (AOR 4.94, 95% CI 1.57–15.59, p=0.006). Professional role (resident versus nurse) remained significant (AOR 3.65, 95% CI 1.16–11.43, p=0.027). Notable gaps included humidification indications (17.6% correct) and recognition of risks from prolonged low-dose oxygen (43.5% correct). Conclusion: Satisfactory knowledge regarding oxygen therapy was observed in only three out of five emergency department clinicians, with significant professional disparities. Training and guideline availability emerged as modifiable factors strongly associated with knowledge. Mandatory in-service simulation-based training programs and the implementation of accessible oxygen therapy protocols are required to optimize patient safety in this and similar high-acuity settings.