A novel gas-liquid reactor is described, in which the two phases flow in annular flow through a number of units consisting of a venturi followed by a twisted tape inserted in the pipe; the former causes significant droplet formation while the latter re-deposits the droplets on the tube wall. Experiments in a 38 mm pipe, with a 19 mm venturi throat, show that up to 35% of the liquid can be atomized, at the cost of an irreversible pressure drop of 0.2-0.3 bar. The extent of liquid-film controlled reaction, measured both with O-2/Na2SO3 and CO2/NaOH, is greater than predicted by a simple theory which regards the drops as rigid spheres, while the gas-film controlled reaction measured with HCl/NaOH suggests a Sherwood number of about 2.5, a little lower than expected. Part of the discrepancy in the former case is due to neglect of absorption in the annular him; the rest may be due to droplet coalescence, for which evidence is available in the literature.