Experiments of synergistic inhibition effects by N-2 or CO2, and ultrafine water mist on methane/air explosion were carried out in a semi-confined transparent explosion vessel. The maximum flame propagation speed, maximum temperature, and maximum overpressure were found to be significantly decreased in the presence of a lower amount of gas-liquid two phase medium. It was also found that the CO2 had a better synergistic inhibiting effect with the ultrafine water mist than the N-2. In the present study, 14% N-2 or CO2 and 2 min mist spraying time were necessary to achieve better inhibition effects, such as declines of the maximum overpressure were 69.8% and 74.4%; and the declines of the maximum temperature were 43.4% and 51.9%; and the maximum flame propagation speed was between 2.13 m.s(-1) and 3.6 m.s(-1), respectively. The experimental results obtained from the present study could potentially facilitate the designs of explosion suppression engineering using water mist inerting systems. (C) 2016 Elsevier Ltd. All rights reserved.