The influence of individual and binary adsorption of octylphenol decaethylene glycol ether (Triton X-100) and dodecyl trimethyl ammonium chloride (DTMAC) surfactants with bulk compositions within (1.50.10(-6) to 4.80.10(-4)) mol.L(-1) on the interfacial tension of a recommended system for liquid-liquid extraction investigations, toluene + water, at 25.0 degrees C is studied. The drop-weight method has been used to measure the interfacial tension, and a maximum relative standard deviation of +/- 0.01 has been appropriate for the concentration of surfactant solutions. From the data and in agreement with the commonly used Szyszkowski equation, a much higher adsorption effectiveness and adsorption tendency for Triton in comparison with DTMAC is obtained. The influence of DTMAC in lowering interfacial tension can be enhanced significantly by adding Triton with bulk mole fraction less than 0.01. For bulk mole fractions up to about 0.2, the estimated interfacial composition and attractive interaction from the theory of nonideal interactions in binary mixtures show different trends. Accordingly, the attractive interaction parameter finds a maximum absolute value at the bulk mole fraction of about 0.01 and lower values at bulk mole fractions between 0.05 and 0.1. Moreover, investigations on the experimental and ideal area per molecule at the interface show variations in agreement with the interaction parameter.