An apparatus for contacting large volumes of gas and liquid together on a microscope scale for mass transfer or transport processes wherein the contact between liquid and gas occurs at the interfaces of a multitude of gas bubbles. Multiple porous tubes assembled in a bundle inside a pressure vessel terminate at each end in a tube sheet. A thin film helical liquid flow is introduced into the inside of each porous tube around and along its inside wall. Gas is sparged into the porous media and the liquid film so that an annular two phase flow with a uniform distribution of tiny gas bubbles results. The gas flow is segregated from the liquid flow without first passing through the porous media and through the liquid film. Nozzles at the lower end of the tubes divert liquid flow to a vessel and redirect the gas flow in a countercurrent direction.