A mathematical model for the supercritical antisolvent (SAS) process is presented and solved numerically. This model takes the main physical phenomena involved in this process into account, including jet hydrodynamics, mass transfer, phase equilibrium, as well as nucleation and crystal growth kinetics. The model allows to calculate the particle size distribution and the yield of the precipitation. The main innovation of this model concerns jet hydrodynamics, which is considered as the mixing of two completely miscible fluids forming a gaseous plume, and is modeled with a k-epsilon turbulence model. The model has been used to analyze the mechanism of particle formation in the SAS process, and to study the effects of the operating parameters on particle size and solid recovery. The comparison with experimental results shows good agreement in the trends. Particle size cannot be predicted accurately due to the lack of knowledge of some parameters of the model. (C) 2004 Elsevier B.V. All rights reserved.