Introduction: Conventionally either partial rebreathing mask or nonrebreathing mask can be used to deliver oxygen concentrations of up to 60%. A simple modification of the partial rebreathing mask using two pieces of respiratory tubing, or ‘tusks’ has been shown to deliver a high FIO₂. Aim: This study aimed to evaluate the efficiency of the ‘tuskmask’. Methods: This was a prospective study. Twenty patients of either gender, 18-70 years, ASA PS I or II and scheduled for elective surgery requiring arterial blood pressure monitoring intraoperatively were studied. On the day of surgery, in the operating room, after establishing standard monitoring, an intravenous access was secured. The radial artery was cannulated using a 20 G cannula and hep-locked. A baseline arterial blood gas (ABG) sample was drawn on room air and three more samples taken after breathing oxygen through a 60% Venturi mask, polymask (10 L/min) or tuskmask (10 L/min) for ten minutes each with a ten minutewashout period in between. The ABG samples were analysed at the end of study. Results: The mean age (SD) in years was 53.65 (17.10). There were 15 female and five male patients. The PaO₂ obtained with tuskmask was significantly higher with tuskmask compared to polymask and 60% Venturi mask but PaCO₂ was similar with all three masks. The mean (95% confidence interval) derived FIO₂ of tuskmask was 0.924 (0.872 to 0.97). Conclusion: The tuskmask when used with oxygen flow of 10 L/min, consistently delivers a very high concentration (FIO₂ ≥ 0.85) without causing rebreathing.