The influence of interfacial properties in oil agglomeration of coal has been experimentally studied by testing four coals of different rank using a series of agglomerating agents obtained by mixing, in variable proportions, two basic commercial oils having distinct densities. The results show that oil agglomeration is always more efficient on coals of higher rank for which fuel recovery can be increased by using suitable mixtures of basic oils. The improvement in recovery is much more marked in the case of subbituminous coals. The experimental results are discussed and a scientific interpretation is given.