BACKGROUND: Administering oxygen therapy (OT) has an essential role in preventing/managing hypoxemia in both acute and chronic conditions. It should be adjusted to achieve the normal oxygen saturation of 94%–98% in most cases. This study aims to evaluate knowledge, attitude and practice (KAP) of nurses, paramedics, emergency medical technicians (EMTs) and Emergency Medical Services (EMS) physicians working at emergency departments (ED) in Riyadh, Saudi Arabia. METHODS: In this cross-sectional study, a structured questionnaire was used to assess KAP related to OT of nurses, paramedics, EMTs and EMS physicians currently working at an ED of a tertiary care hospital. Knowledge and attitude were assessed using a Likert scale from 1–5, whereas practice was assessed as a yes/no categorical variable. RESULTS: A total of 444 emergency health-care workers (EHCWs) participated, of which 225 (50.7%) were male, with the majority (77%) in the age group of 20–35 years. Over half of the sample were nurses (266; 59.9%). The mean score for knowledge about OT was 5.51±1.45, attitude was 26.31±3.17 and for practices 4.55±1.76. The main factors which were associated with poor KAP were workload and lack of local guidelines. The distribution of overall practice score was significantly better among paramedics – nurses group and EMT – nurses group. CONCLUSION This study demonstrates that there is a gap in EHCWs' KAP, particularly regarding when to provide OT to a patient. This gap can affect patients' safety. Extensive educational and training programs about OT are needed to raise awareness among health-care providers.