Abstract An apparatus and procedure is described for growing a bubble of one fluid with constant radial velocity between parallel solid plates, so displacing a second fluid. The process can be reversed, so that both advancing and receding angles can be studied as a function of the interfacial velocity. Results are given for the displacement of saturated air by water between siliconed glass plates at 22° and 42°C., and between polyethylene plates at 22°C. The displacement of a water-saturated hydrocarbon oil between siliconed glass plates by oil-saturated water, and by an aqueous potassium laurate solution, has also been studied at 22°C. In all systems, a definite dependence of the advancing and receding contact angles upon the interfacial velocity is found, except at very low speeds, and a provisional interpretation is given.