A quantitative theory is developed to describe the dynamic surface tension and the adsorption kinetics at a liquid-liquid interface, taking into account the molecular diffusion in both bulk phases and the adsorption isotherm for surfactant on the interface. Asymptotic analytical solutions are obtained in the following finite systems : (i) a liquid spherical drop, (ii) a liquid spherical drop surrounded by a liquid phase, and (iii) a liquid spherical drop surrounded by a spherical liquid shell. The behavior of the dynamic surface tension and interfacial adsorption over a wide range of times is predicted for cases (i) through (iii). The conditions under which the dynamic surface tension passes through a minimum below the steady state value are found. The theoretical model developed allows a qualitative interpretation of the experimental data obtained for a viscous crude oil containing natural acids after contact with aqueous alkali.