This proposal aims to expand knowledge about water-in-CO2(w/c) microemulsions by studying the ¿bending rigidity¿ of surfactant films, which has been frequently tested on normal liquid microemulsions [e.g. 1-8], and is recognised as a very useful method to correlate optimal surfactant chain length with phase stability. Herein, is described a designed experiment to overcome the technical difficulties of matching the contrast between the water core and bulk in w/c microemulsions, which will enable, for the first time to determine the film bending rigidity in such systems. This proposal is a resubmission for an earlier one (RB1320006). As requested by the sub-committee, preliminary experiments on analogous liquid phase water/heptane microemulsions have now been conducted. These new results validate the approach proposed for determining film properties in the more the challenging w/c systems.