Results are presented of studies on the mutual volumetric ratios of solid, liquid and gaseous phases in the three-phase froths formed during the coal flotation process. It was shown that these ratios are significantly dependent on the concentration of solid phase in the floated coal slurries suspensions, the coal rank, the composition of the flotation agent and in particular the volume of promoter it contains. These variables also influence that important technological parameter, content of solid parts in the froth product suspension. The relations ascertained were corroborated by the results of industrial trials.