Abstract: The objectives of the present invention are achieved by preparing a foamable composition comprising a viscous liquid and a gas homogeneously dispersed in the liquid. The compositions are prepared by blending a pressurized gas with the viscous liquid in a mixing chamber. In accordance with the present method the flow rate of the pressurized gas into the mixing chamber is controlled as a function of the flow rate of at least one high viscosity liquid into said chamber. The apparatus includes a means for controlling the flow rate of the pressurized gas as a function of either the difference in the feed pressures of said gas and said liquid or a predetermined ratio of the volumes of liquid and gas present in said mixing chamber.