Water solubilization by anionic perfluorinated surfactants has been examined in the condensed phase of the hydrofluorocarbon (HFC) gas 1,1,1,2-tetrafluoroethane (R134a) in the temperature range 15-55 degreesC and to pressures of 500 bar. The surfactant di(1H,1H,5H-octafluoro-n-pentyl) sodium sulfosuccinate (di-HCF4) forms stable water-in-R134a microemulsions up to w > 60 (where w = [H2O]/[surfactant]) with applied pressure and to w = 50 at the vapor pressure of R134a. Solubilization levels for the related surfactant di(1H,1H,5H-octafluoro-n-pentyl) ammonium phosphate and the commercial grade anionic perfluoro poly-(propylene oxide) carboxylate (CF3(CF2CF(CF3)-O-)(3)CF2CO2-NH4+) were lower. Structural features of the microemulsion systems formed have been examined by small-angle neutron scattering (SANS). The SANS data from all microemulsions examined were characteristic of spherical droplet structure and provided measurement of the mean radius and, for di-HCF4, the headgroup area at the water-R134a interface. When significant, attractive interactions between droplets were evident in the S(Q)(ATT) contribution to the SANS I(Q). The low level of this contribution for di-HCF4 confirmed the good compatibility of this surfactant with R134a under the conditions examined.