A rectangular Pyrex glass reactor was indirectly sonicated with a 65-mm-diameter 200 kHz transducer under batch and flow conditions at 20 degrees C and then partitioned using Perspex plates and sonicated again. Both the degradation of methyl orange (MO) and the calorimetric power decreased with partitioning. Under batch conditions, as the number of compartments increased from 1 to 7, the MO removal efficiency (RE) decreased from 83% to 45%, and the pseudo-first-order rate constant (k) decreased from 0.097 to 0.034 min(-1). Under flow conditions the MO RE also decreased from 66% to 27% as the number of compartments increased, and k decreased from 0.096 to 0.016 min(-1). Partitioning reduced the reactor volume and contributed to acoustic energy attenuation, resulting in decreased reactor performance, where MO RE was affected by the cross-sectional area, flow velocity, and solution volume.