The solubilization of molecules into surfactant micelles is a known and studied phenomenon. A newer phenomenon, the solubilization of solutes into adsorbed surfactant aggregates at the solid/liquid interface, called adsolubilization, is the surface analog of solubilization. Studies of adsolubilization have applications ranging across the fields of environmental remediation, drug adsorption/delivery, catalysis, thin films, engineered surfaces, and advanced oil recovery. A model to predict the full adsorption isotherm would facilitate these studies. Unfortunately, although the amount of experimental data is increasing, the number of variables involved; such as, pH, substrate, amount of adsorbed surfactant, solute size, polarity, etc.; have hindered adsolubilization model development. The main objective of our work is to develop a model for estimating the partition coefficient, Kad, of non-polar, non-ionized solutes between the admicelle and the bulk phase below the CMC, to lay the foundation for a future more universal admicelle model. To achieve this goal, the activities of the solutes partitioning between the aqueous and the admicelle phase was evaluated by treating the admicelle phase as a separate pseudophase. The activity coefficients were predicted with the assumption that the admicelle pseudophase behaves as an alkane phase having the same number of carbons as the surfactant tail group. We modeled the effective molar volumes of the admicelle pseudophase using surfactant loading and head-group properties. Adsolubilization data; for a number of solutes with specified surfactant concentration, pH, ionic strength, and surface substrate; validated the ability of our thermodynamic model to predict the activities of the modeled solutes within the admicelle phase. We modeled relationships between Kad and solute concentration using the following activity coefficient models Wilson, Scatchard-Hildebrand, UNIFAC, and UNIQUAC. Solutes modeled included acetophenone, benzene, naphthalene, styrene, and toluene.