Abstract: A method and apparatus for contacting a gas and liquid. An elongated cylindrical reactor has an inlet region of reduced cross-sectional area at a first end. At least some of the gas or liquid is introduced into the inlet region in a direction tangential to the longitudinal axis of the reactor by way of an inlet to cause rotational flow within the inlet region. The gas or liquid flows into the remainder of the reactor at such a velocity as to cause more intimate mixing of the liquid and gas. Additional gas or liquid can be introduced through a second inlet disposed in an intermediate region of the reactor so that the fluid introduced flows in a generally longitudinal direction or rotational direction.