We have developed a new series of branch-structured anionic surfactants dissolved significantly well in sc-CO2. We found that, the variation of counter ion species has a significant effect on the solubility of the surfactants in sc-CO2. Among these, the solubility of surfactant with ammonium ion exceeded 16 wt% at 40 degrees C and 15 MPa while that of surfactant with K+ was neglectable. This effect can be used for complete recovery of the surfactant.