We investigate the effects of size and energy parameters and dipole moment of co-solvent molecules on the solute residual chemical potential in infinitely dilute supercritical fluids. To determine the chemical potential, an NPT test-particle computer simulation method is employed. Both polar and nonpolar co-solvent are considered. The results show that the Lennard-Jones (LJ) energy parameter of the co-solvent greatly affects the solubility of the solute whereas the size parameter does not. For the system containing polar co-solvent and polar solute, we find that a larger co-solvent dipole moment enhances the solute solubility. By comparing the solute chemical potential reduction due to the long range dipole-dipole interaction with that due to the short range LJ interaction, we also find that the local molecular interaction dominates the value of the solute residual chemical potential.