A new experimental methodology has been developed to measure bulk mass densities and interfacial tensions of mixtures at vapor-liquid-liquid equilibria (VLLE). This technique considers the use of a combined device that includes a vibrating tube densimeter connecting to a pendant drop tensiometer. This methodology is applied to four ternary mixtures of water + n-hexane + alcohol (ethanol or n-butanol) and water + MTBE + alcohol (ethanol or n-butanol) at VLLE. Complementarily, the measured data are modeled by the Square Gradient Theory coupled to the volume translated Peng-Robinson equation of state, which provides information about unmeasurable interfacial concentration profiles. According to the experimental results, bulk phase densities and interfacial tensions are obtained within acceptable statistical deviations, where the interfacial behavior is governed by the mass bulk density. Based on the theoretical results, bulk densities are in good agreement to the experimental determinations, whereas interfacial tensions are obtained within good agreements for the vapor-aqueous interface, acceptable statistical deviations for the vapor-organic interface but high deviations are observed in the aqueous-organic interface. The interfacial concentration shows different patterns that change with the type of interface and temperature, observing high adsorption of alcohols, moderate for ether, and no adsorption for water and n-hexane.