Introduction: The two-level noninvasive positive pressure ventilation (NPPV) is the most commonly used mode of ventilation in the treatment of early respiratory failure. During NPPV, the inspired oxygen fraction (FiO₂) could be influenced by various factors such as the inspiratory positive airway pressure (IPAP), the expiratory positive airway pressure (EPAP), the O₂ flow rate and the site where O₂ is added to the circuit. Aim: To investigate the effect of IPAP, EPAP, O₂ flow rate, leak and the O₂ injection sites on the fraction of delivered oxygen (FDO₂). Methodology: A lung model was constructed to simulate noninvasive ventilation with bilevel positive airway pressure (BiPAP) without leak and with 10% leak, the oxygen analyser was placed proximal to the ventilator to measure FDO₂ when oxygen was injected at three different sites. The portable BIPAP device was set to spontaneous/timed mode. Inspiratory and expiratory pressures of the BIPAP device were set at 10/5, 15/5, 15/10 and 20/10 cm H2O. Results: This study revealed that there is a variation in the FDO₂ with a change in the position of connection of oxygen tubing, leak in the system and the oxygen flow rate. Conclusion: During NPPV, the FDO₂ varies significantly with O₂ flow rate and presence of leak. Higher O₂ flow rates and lower amounts of leak provide a higher FDO₂. Higher FDO₂ is achieved if the oxygen tubing is connected proximal to the patient whereas the effect of ventilator settings on FDO₂ is not significant.