This proposal aims to explore cheap and environmental-benign cosurfactants (or cosolvents) for yielding CO2-philic hydrocarbon surfactant/water/CO2 microemulsions (W/CO2 microemulsions) at high water-to-surfactant molar ratios (W0), under mild pressure (P) and temperature (T) conditions. In close collaboration, University of Bristol and Hirosaki University (Japan) have been developing new, very promising hydrocarbon surfactants for W/CO2 microemulsions (Table 1). The high-pressure SANS (HP-SANS) experiments proposed will permit an exploration of surfactant+co-surfactant synergism in W/CO2 microemulsions, potentially leading to cheap and environmental-benign W/CO2 microemulsions which can form under mild conditions.