A one-phase microemulsion composed of a hybrid fluorocarbon/hydrocarbon surfactant C7F15CH(OS0(3)(-)- Na+)C7H15, water, and CO2 solubilizes substantial amounts of water. For example, the water-to-surfactant ratio in a single phase microemulsion is as high as 32 at 25 degrees C and 231 bar, compared with a value near 0 for more than 150 previously studied surfactants for temperatures up to 50 degrees C. Also with 1.9 wt % surfactant, up to 2 wt % water is soluble, which is 10 times the amount soluble in pure CO2. The requirements for the design of surfactants that form microemulsions in CO2 are examined.