In our previous paper, a new experimental technique based on the potentiometric method was developed to obtain thermodynamic activity data (in form of activity ratio) particularly for ternary electrolyte+nonelectrolyte+H2O solutions supersaturated with the nonelectrolyte. In this paper, a rigorous thermodynamic approach is proposed to derive activity data for binary nonelectrolyte+H2O solutions in the supersaturated region, via cell potentials of an electrolyte tracer and solubility data of the nonelectrolyte. An analysis of thermodynamic consistency is presented to evaluate the reliability and accuracy of the measured data. A systematic experimental investigation of three ternary electrolyte+nonelectrolyte+H2O and two binary nonelectrolyte+H2O systems is reported in both under-saturated and supersaturated regions (up to a supersaturation level of approximately 27%). Interesting thermodynamic behaviors are observed and their significance is discussed, with the role of thermodynamics in exploration of crystallization phenomena highlighted. (C) 2009 Elsevier Ltd. All rights reserved.