The industrial application of supported liquid membranes (SLMs) is still limited due to concerns about their stability. In a previous work, the selective separation of the substrates and products of a transesterification reaction was successfully carried out using Nylon membranes impregnated with ionic liquids (ILs). This article analyses the effect of both the IL composition and the nature of the surrounding phase on the stability of these SLMs to design highly stable supported ionic liquid systems. For this purpose, the stability of SLMs based on several ILs after immersion for a week in different feed/receiving phases was characterized using scanning electron microscopy combined with energy dispersive X-ray (SEM-EDX). The differential migration of the ILs observed from the membrane toward the surrounding phases was found to be correlated with the solubility of the ILs in the contacting phases. It was observed that SLM stability increased as the polarity of the solvent used as receiving phase decreased and as the hydrophilic character of the ILs used as liquid phase increased. Furthermore, the polymeric support was found to have a strongly stabilizing effect because losses of IL after immersion in a given surrounding phase were much lower than that derived from the solubility of the IL in this phase. (C) 2011 American Institute of Chemical Engineers AIChE J, 58: 583-590, 2012