Fourier transform infrared (FT-IR) spectrum of water-in-supercritical CO2 microemulsion was measured at 60 degrees C and 30.0 MPa over a wide range of water/CO2 ratio from 0.0 to 1.2 wt % to study the distribution of water into CO2, interfacial area around surfactant headgroup, and core water pool. The microernulsion was stabilized by sodium bis(1H,1H,2H,2H-lieptadecafluorodecyl)-2-sulfosuccinate [8FS(EO)(2)] equimolarly mixed with sodium 1-oxo-1-[4-(tridecafluorohexyl)phenyl]-2-hexanesulfonate [FC6HC4] or with poly(ethylene glycol) 2,6,8-trimethyl-4-nonyl ether [TMN-6]. The signal area of the O-H stretching band of water suggested that the number of water molecules in the microemulsion increases linearly with the water/CO2 ratio, except for a slow initial increase below 0.4 wt % due to a part of water dissolved in CO2. The amount of water in CO2 was evaluated by decomposing the bending band of water into two components, one at lower frequency ascribed to water in CO2 and the other at higher frequency to water in the microemulsion. The decomposition confirmed that CO2 is saturated with water at the water content of 0.4 wt %. It was also revealed, from the symmetric S=O stretching frequency of the surfactant, that the sulfonate headgroup is completely hydrated at the water/CO2 ratio of 0.4-0.5 wt %. The results demonstrated that water is introduced preferentially into CO2 and the interfacial area at small water content, and then is loaded into the micelle core after the saturation of CO2 with water and the full hydration of the surfactant headgroup.