A set of analytical equations is derived for the estimation of the average diameter attained by particles that are generated by the rapid expansion of a supercritical solution (RESS). Applying the simplified model to one specific, but nevertheless representative set of experimental conditions for RESS processing, theoretical findings from earlier work could be generally confirmed and new insight was gained. Particles generated by RESS through an expansion device having a cylindrical section with a small aspect ratio will generally not attain average diameters of more than 20-50 nm before passing through the critical cross section since the time available for growth by condensation is limited to a few microseconds. Comparing three different driving mechanisms for growth due to coagulation, it was found that the effects of slip flow differences can be seen as most promising to significantly improve existing RESS models. (c) 2006 Elsevier B.V. All rights reserved.