We report on how salts from the Hofmeister series as well as common sugars alter the aqueous interfacial free energy of aliphatic and aromatic hydrophobic surfaces. We prepared self-assembled monolayers (SAMs) which present a hydrophobic group, and measured the interfacial free energy, through adhesion measurements in a chemical force microscope, for a variety of solutions at high concentrations of 1 to 5 M. The cosolvents studied range from protein stabilizing to denaturing agents. Experimental results of the interfacial free measurements are critically compared to single molecule transfer free energy measurements, as well as computational studies of hydrophobic surfaces.