Introduction: Bag-mask ventilation does not always guarantee 100% seal around airway opening and hence delivered fraction of oxygen (FDO₂) may vary. Aim: To determine the FDO₂ via a standard neonatal selfinflating bag with and without application of leak, without a reservoir bag with flow rates of 0.1, 0.2, 0.4, 0.6, 0.8, 1, 2, 4 and 6 L/min. Method: A test lung with a three way rotator to produce 0%, 30%, 50% and 75% leak was connected to a 3.5 mm ID endotracheal tube (ETT) connected to a VBM standard preterm self-inflating bag of 250 mL without a reservoir. The ETT was connected to ENVENTEC oxygen analyser and the bag inlet to a 100% oxygen source. Ventilation was done to a peak pressure of 15-20 cm H₂O, at 40 bpm. FDO₂ was recorded every 30 s, until the difference between two consecutive values was ≤1%. Result: The change in FDO₂ was maximum when compared between 0.1 L/min and 6 L/min. For all leak percentages, the delivered oxygen showed an increasing trend from 0.1 to 0.6 L/min, a plateau from 0.6 to 1 L/min after which it increased. The change in FDO₂ was different for different flow rates among various leak percentages. The highest delivered oxygen without leak was 56.15 ± 3.45% with 4 L/min flow. The oxygen delivered with 70% leak was considerably lower when compared to values with different leaks with respective flow rates. Conclusion: FDO₂ increases with oxygen flow rates greater than 1 L/min. Leak around the mask has no effect of FDO₂. Equilibration of FDO₂ is achieved with in 60-90 s.