A new linear approximation for a mixed-controlled adsorption process had been designed for estimating the surfactant diffusivity (Df) and adsorption rate constant (βf) by purely using the dynamic surface tension (ST) data (Moorkanikkara and Blankschtein, 2006). However, the uniqueness and applicability of this linear approximation are yet to be ascertained. Subsequently, a theoretical simulation was conducted to study the uniqueness and robustness of this linear approximation. An adsorption process of nonionic surfactant onto a freshly created planar air-water interface was considered and its mixed-controlled dynamic ST profiles were simulated using the Langmuir model. Linear regions in the simulated ST vs t1/2 profiles do exist, which could be described well by a straight line with an intercept >72 mN/m (representing the linear approximation). Values of Df and βf could then be estimated from the slope and the intercept of this straight line. While the applicability of this linear approximation was confirmed, the results did show a distinct possibility of obtaining multiple sets of Df and βf if different linear regions of the γ vs t1/2 profiles were selected for the fitting. Additionally, the applicability of this linear approximation on experimental dynamic ST data was tested.