The adsorption of C12E4 Onto a fresh air-water interface was investigated by using video-enhanced pendant bubble tensiometry. From the comparison between the equilibrium surface tension data and the theoretical relaxation profiles predicted by the Frumkin adsorption isotherm, the adsorption process was found to be anticooperative. Dynamic surface tension data for C12E4 molecules absorbing onto a freshly created air-water interface for different bulk concentrations were used for the determination of the controlling mechanism and the evaluation of diffusivity. Comparison was made for the entire relaxation period of the surface tension data and the model predictions. It is concluded that the adsorption process is of diffusion control and the diffusion coefficient is 6.4 x 10(-6) cm(2)/s. The lower limit of the adsorption rate constant of C12E4 were obtained from the theoretical simulation. Besides, the pendant bubble, at which the interface had reached the equilibrium state, was expanded rapidly and a relationship between surface tension (gamma) and surface area (A) was obtained. A curve relating gamma and relative surface concentration Gamma/Gamma(ref) was obtained from the gamma-A data and then used to examine the adsorption isotherm utilized in this study.