Experiments of vented gas explosions involving two different cylinder vessel volumes (0.2 and 0.0065 m3) were reported. It was found that self-acceleration and larger bulk flame trapped inside the vessel are the main factor enhancing the overpressure attained in 0.2 m3 vessel. There was about 2 to 7 times increase in ratio of pressure and flame speeds on both vessels at the same equivalence ratio and K which can be considered as turbulent enhancement factor, β. The comparison with previous work has shown over-prediction results as compared to the present study.