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Dynamic interfacial tensions provide insight into the mechanism of surfactant adsorption at and transport across an interface. As an example, the adsorption kinetics and the distribution of a surfactant (alkyl dimethyl phosphine oxide with an alkyl chain length of 13) was studied at the water/hexane interface. The drop shape method used yields dynamic interfacial tensions that pass through a minimum under certain conditions. Model calculations show that depth, width and location of the minimum and the equilibrium adsorption state depend on several parameters: the diffusion coefficients of the surfactant in the two liquids, the distribution coefficient between the phases, the liquids volume ratio, and the total surfactant concentration in the system. One can conclude that surfactants are often soluble in both liquid phases, and transfer across the interface between them has to be considered. If a surfactant is to be optimized in a liquid-liquid system to achieve maximum efficiency of a technological process, the surfactant distribution coefficient plays a significant role.