In batch gas antisolvent (GAS) recrystallization, the gradual addition of CO2 to a liquid solution containing the solute causes the system pressure to rise and the volume of the liquid phase to expand substantially, eventually resulting in solute precipitation. The expansion rate depends on the rate of antisolvent addition and on the vapor-liquid mass-transfer rate and determines the rate of supersaturation buildup in solution, which ultimately controls the particle formation process. We study the effect of mass-transfer resistance on volume expansion, both theoretically by development of a mathematical model of the mass-transfer phenomena under typical GAS recrystallization conditions and experimentally through volume expansion experiments (CO2 in toluene) to assess the role of operating parameters such as stirring rate and aeration mode. A satisfactory agreement between model results and experimental data is achieved in all cases.