An investigation was carried out on the effect of process parameters involved in Pre-Dispersed Solvent Extraction (PDSE) on the stability and interactions in dilute dispersions of Colloidal Liquid Aphrons (CLAs). The aim of this work was to derive empirically-based engineering relationships that could be used in the design of PDSE processes. For this investigation, CLAs were formulated with an Aliquat 336/n-octanol/Softanol 120 solvent phase, and a Synperonic A20 aqueous phase. These CLAs were intended for use in the reactive pre-dispersed solvent extraction of polar solutes such as phenylalanine. Light scattering measurements over a range of continuous aqueous and CLA phase conditions were used as a method of obtaining a measure of the rate of disappearance of CLAs from dispersion (a measure of stability), and a comparison of stability under different conditions. Two forms of CLA interaction occurring by independent mechanisms were identi®ed ± CLA break-up, and CLA ¯occulation. Break-up was found to be a ®rst order process, allowing CLA stability to be characterised by a ®rst order half-life (typical half-life 15±40 min). This was proposed to occur on collision of CLAs with suf®cient energy to overcome the stabilising forces provided by the surfactants at the interfaces of the CLAs. It was shown that ¯occulation occurred at high ionic strengths (b0.1 M NaCl), and that it was not part of the break-up mechanism. An apparent size dependent CLA half-life was proposed to be due to smaller particles having a lower collision energy on average. The data suggested that the resistance to CLA break-up was not charge repulsion, but derived from an interaction between molecules of one of the surfactants making up the aqueous `shell' of the CLAs (Synperonic A20). Finally, the basis for a semi-empirical design equation for prediction of CLA half-life developed from the Arrhenius equation was proposed.