Selective countercurrent transport of dense adsorbent particles through pulsed multistage, liquid fluidized beds of light catalyst particles is attractive as the basis for new countercurrent adsorptive reactors. Its applications are expected to demand operation at high solids flows, and thus at high pulsation frequencies and volumes. The effect of high pulsation frequencies and volumes on the flows of liquid and solids is studied by model and experiment. The key parameter determining contactor behavior is the product of pulsation frequency and volume : the pulsed back flow. Its theoretical maximum (flooding condition) equals the liquid flow rate. High pulsation frequencies and volumes greatly affect the degree of liquid and solids mixing. The degree of liquid mixing increases exponentially with increasing pulsed back flow from plug-flow behavior (Pe = 10-100/stage) to complete mixing near the flooding condition. The solids mixing at low-to-moderate solids transport could be described with complete mixing at this stage. At higher solids transport, the extent of mixing slightly decreases toward two tanks-in-series per stage. The relations established allow for a preliminary design of a pulsed multistage fluidized-bed reactor at any low and high solids transport rate, as well as for the estimation of corresponding operating conditions.