An analysis based on the coupled equations for the penetration model of gas-liquid mass transfer, solution chemistry and the distributed dynamic mass and population balances applied to the crystallization step is used to predict the effect of the gas-liquid mass transfer rate on the precipitation of calcium carbonate at 25 degrees C using equilibrium and kinetic data from the literature. Generally, the nucleation rate in the region close to the gas-liquid interface is predicted to increase with decreasing gas-liquid mass transfer rate; at very low mass transfer rates, nucleation rates are, however, inhibited by the depletion of Ca2+ ions. Under conditions of low mass transfer rates, nucleation proceeds predominantly in the interfacial region rather than in the bulk solution. Nucleation rate, particle number density and mean particle size are predicted to exhibit a maximum with position away from the gas-liquid interface.