This paper describes the effect of volatility on residence time distribution and conversion in multiphase reactors. This is relevant for the many processes where substantial vaporization of the liquid feed occurs. The typical situation is that the evaporated molecules not only lower the concentration in the liquid phase but also travel faster through the reactor. Our complete model uses two mobile zones, one for the liquid phase and one for the gas phase, with dispersion in each zone and mutual mass transfer. In short, this work can be thought of as extending the popular Piston-Dispersion-Exchange model by adding mobility and dispersion to the second zone. We explore the entire parameter space for our model numerically. We describe quantitatively how the mean residence time of a component decreases when it significantly evaporates to a faster-moving gas phase. We explore how slow mass transfer contributes to the broadening of the residence time distribution. Experimentally, we validated the model in a more limited parameter space in a gas-liquid micro-packed bed with volatile compounds(isopentane, pentane, and 2,2 dimethylbutane) and non-volatile compounds (1-methylethyl benzene) in different solvents (tetradecane and 1-nonanol). The effect of volatility on conversion was analyzed for an (n) under bar (th)-order liquid-phase reaction at different mass-transfer rates. Wherever possible, we extract from the detailed numerical model practical engineering correlations for average residence time and conversion. The results presented in this work teach whether reactant volatility should be considered in a reactor design. (C) 2010 Elsevier Ltd. All rights reserved.