The time-averaged power dissipation rates and gas holdups have been measured in a 15 cm diameter glass column provided with reciprocating doughnut baffle plates (internal diameter 7 and 9 cm). Most of the data were obtained at a reciprocation frequency of 5 Hz with amplitude in the range 1 to 10 mm. The continuous phase was water and the dispersed phase was air, supplied at superficial velocities mainly in the range 0.32 to 1.14 mm s(-1). The power dissipation rates agreed with previously proposed models; the quasi-steady state model at high amplitudes and the acoustic model at low amplitudes. The pressure/displacement wave forms for the plate stack were affected by dispersed gas. The gas holdup was increased strongly by reciprocation, with entrainment of gas bubbles into the vortices that formed at each plate. The doughnut plates are more effective, for a given power input, than conventional plates with multiple perforations reported in previous literature.