Abstract: The separation of dispersions in emulsions by passing through a coalescing fibrous bed has many advantages over other types ot separation methods in its simplicity and efficiency. A thermodynamic term, the difference in the work of wetting, which characterizes the difference in fiber wettability by the continuous and dispersed phases is presented in this paper. It can be used as an important criterion for the correct selection of fibre media to obtain a high degree of coalesence. Furthermore, several kinds ot commercial fibres were investigated for treating oil in water emulsions. It was found that polypropylenc fiber had an excellent coalescence efficiency.