In order to investigate the effects of the humidity, temperature and slow oxidation reactions on the occurrence of explosions in gasoline-air mixtures, experiments are carried out in a cylindrical tunnel with a solid heating device. Experimental results show that whether a gasoline-air explosion occurs or not is determined by a critical relative humidity when the temperature of the heat source is maintained at a specific value. Under the experimental conditions in this study, when the heat source temperature is maintained at 550℃, the critical value of relative humidity is 32.3% ± 0.2%, and when the heat source temperature is maintained at 570℃, the critical value of relative humidity climbs to 37.7% ± 0.2%. The occurrence of gasoline-air explosions is very sensitive to the gas mixture temperature. It is shown that an explosion will not occur if the gas mixture temperature is lower than the critical value of 26℃. Influenced by slow oxidation reactions, concentrations of reactants can decrease below the explosion limit range, resulting sometimes in no observed occurrence of gasoline-air explosions. Experiments show, in this case, that the critical heat source temperature for the gas mixture explosion, defined by a probability of explosion occurrence of 20%, climbs from 510 to 550℃, i.e. it increases 40℃ solely due to the influence of slow oxidation reactions.