The adsorption kinetics of beta-casein, BSA, and lysozyme at the air-water interface were compared with those at the triolein-water interface. The rates of adsorption of B-casein, BSA, and lysozyme to the oil-water interface were consistently higher by an order of magnitude, compared to the respective bulk diffusion coefficients. The rates of adsorption of beta-casein and BSA to the air-water interface were, however, closer to the respective bulk diffusion coefficients, while that of lysozyme to the air-water interface was an order of magnitude smaller than its hulk diffusivity. Also, the equilibrium concentrations of the three proteins at the oil-water interface were several times higher than those at the air-water interface. The remarkable differences in the rates of adsorption of the three proteins, particularly lysozyme, at these interfaces were unequivocally explained by differences in the potential energies of interaction of the proteins with these two interfaces. Potential energy calculations showed that dispersion interactions between proteins and the oil-water interface is attractive, whereas those between proteins and the air-water interface were generally repulsive. Thus, the slower rate of adsorption of proteins to the air-water interface may be attributed to the dominating repulsive dispersion interactions. In addition, the existence of an energy barrier in the potential energy profile of lysozyme as it approached the air-water interface conclusively explained its unusually slow adsorption rate and the presence of a long lag period (60 min) for its adsorption to commence at the air-water interface.