We examined the ability for microemulsion formation of fluorinated surfactants containing perfluoropolyether moieties for the CO2-philic tail group and carboxylic acid ammonium or poly(ethylene glycol) methyl ether for the hydrophilic.groPps and found that the hydrophilic CO2-philic balance of surfactants plays an important role in the formation of microemulsions. system. A weighed amount of surfactants (2 wt% for CO2) was introduced to the cell, and the cell was sealed. Carbon dioxide was poured into the cell, and the cell was heated to experimental temperature. In this study, the formation of a clear mixture that contains water rather than the solubility to the pure CO2 was regarded as the formation of microemulsion.