Out-of-hospital cardiac arrest (OHCA) is common and carries a high mortality rate. In Victoria, Australia approximately 50% of patients with an initial cardiac rhythm of VF achieve a return of spontaneous circulation (ROSC) and 30% overall survive to hospital discharge. Currently, OHCA patients who have achieved ROSC but who remain unconscious routinely receive 100% oxygen for several hours in the ambulance, ED, cardiac catheterisation laboratory until admission to ICU. However, there is now evidence from laboratory studies and preliminary observational clinical studies that the administration of 100% oxygen during the first few hours following resuscitation may increase both cardiac and neurological injury. Clinical trials are underway to test whether titrated oxygen to a target oxygen saturation of 90-94% in the immediate hours after ROSC results in improved outcomes compared with 100% oxygen.