This investigation has been aimed at developing a method for characterizing and predicting the performance of collectors based on pressure-area isotherms. This procedure can be used both to choose the proper collector and to develop effective new compounds by determining the effect of changes in interfacial properties. The surfactant activity of the collector is dependent on the bulk phase behavior of the chemical when dispersed in a three-phase system. This behavior can be monitored by determining the collector surface pressure isotherms for adsorption at the interface. Further, collector adsorption is dictated by bulk physical properties of the collector. These properties are described and discussed. This paper presents a technique with which a modified Langmuir film balance may be used to study the effectiveness of a collector for maximum floatability in terms of grade and recovery. Experimental data are presented for sulfide ore. Collectors chosen are those which are already tested for flotation performance. Strong correlations were obtained between a collector performance and film pressure. A careful selection of solvent can significantly improve the surface activity of the collector. It is proposed that the correct solvent is one which allows the collector to dissolve totally without irreversible aggregation. The consequences of this selection of a solvent are improved surface activity and collector performance.