The maximum rates of pressure rise of propylene-air explosions at various initial pressures and various fuel/oxygen ratios in three closed vessels (a spherical vessel with central ignition and two cylindrical vessels with central or with top ignition) are reported. It was found that in explosions of quiescent mixtures the maximum rates of pressure rise are linear functions on total initial pressure, at constant initial temperature and fuel/oxygen ratio. The slope and intercept of found correlations are greatly influenced by vessel's volume and shape and by the position of the ignition source - factors which determine the amount of heat losses from the burned gas in a closed vessel explosion. Similar data on propylene-air inert mixtures are discussed in comparison with those referring to propylene-air, revealing the influence of nature and amount of inert additive. The deflagration index KG of centrally ignited explosions was also calculated from maximum rates of pressure rise. (c) 2006 Elsevier B.V. All rights reserved.