The adsorption of sodium oleate and various ethoxylated nonylphenol surfactants and their mixtures at air/liquid interface was investigated by equilibrium and dynamic surface tension experiments. Synergism was determined by observing the lowering of surface tension of water by single surfactants and their mixtures. The results showed that the addition of nonionic surfactant reduced both the equilibrium and dynamic surface tension of sodium oleate solutions. The effect of molecular weight, HLB, and degree of ethoxylation of the surfactant was studied. Interaction between anionic and nonionic surfactant mixtures was calculated by using an interaction parameter. The interaction parameter between oleate and NP-4 (a nonionic surfactant) was calculated to be -0.21, showing attraction between the two surfactant molecules.