The expansion of a supercritical fluid (SCF) solution composed of CO2 and naphthalene from 10 to 1 MPa has been simulated by using both the conventional NVT-MD and one-dimensional pressure-control molecular dynamics (OPC-MD) methods. The characteristic pressure corresponding to a significant decrease in density of the SCF solution (about 6 MPa) is lower than that of pure CO2 (about 8 MPa) due to the strong attractive interactions of NAP molecules with CO2 molecules. The solute clusters dispersed in the SCF start to grow at the characteristic pressure by uniting small clusters to form a larger cluster and gathering dispersed solute molecules to the cluster. In the solute clusters, the number of CO2 molecules gradually decrease as the clusters grow, though the number is still comparable to that of solute molecules at 1 MPa, suggesting that remaining CO2 molecules will escape from the solute clusters at lower pressures. (C) 2004 Elsevier B.V. All rights reserved.