The effects of heterogeneous oxygen groups of activated carbon on the adsorption of dissolved phenol in single and mixed solvents have been studied. Cyclohexane, heptane, and mixtures of cyclohexane and heptane with different volumetric ratios have been used as solvents. Solvent hydrophobicity, the capability of the molecules to H-bond, and dispersive/repulsive interactions were found to be the main factors that affect the adsorption capacity. In a homogeneous mixed solvent, all phenol isotherms were very close to the pure heptane rather than pure cyclohexane isotherm for the untreated carbon, which has the lowest surface oxygen concentration. However, as the concentration of surface oxygen increases, phenol isotherms from the mixed solvents are more evenly distributed. It is suggested that selective segregation of the different solvents molecules (cyclohexane and heptane) can occur in the adsorbed phase based on differences in hydrophobicity between solvent molecules.