Abstract The preferential adsorption of n-decanol, n-decylamine, n-decanoic acid, and ethyl octanoate from binary solutions with heptane onto alumina was studied. The net surface excess isotherms were measured for each system and resolved into component isotherms. The effect on the resolved isotherms of the cross-sectional area assumed for the polar adsorbate molecules is illustrated. The heat of immersion was measured in the n-decanol, n-decanoic acid, and ethyl octanoate solutions. Heats of immersion support the net and resolved isotherms. The alumina surface immersed in n-decanol/heptane and in ethyl octanoate/heptane solutions was found to be heterogeneous when analyzed in terms of a theoretical model.