The influence of the phase behaviour of the solvent-anti solvent system on the process conditions for the gas-antisolvent process is investigated. The two fluids are modelled by the Peng-Robinson equation of state while the dissolved solid is described by a Clapeyron-type approach. Based on the correlation of the ternary system, a liquid-liquid immiscibility region has been found which hinders the proper crystallisation of the solute. A thorough investigation of the binary solvent-antisolvent system by the global phase diagram methods yields a criterion for the proper choice of the solvent. The crucial property turns out to be the distance of the sol vent-anti solvent system from the tricritical curve in the global phase diagram. (C) 2004 Elsevier B.V. All rights reserved.