The performance of four different shaped sonochemical reactors (cylindrical, conical, double cone and pyramidal) were characterized in terms of residence time distribution, calorimetric energy efficiency and methyl orange degradation under three flow rates (10, 20, and 30 mL min(-1)) and two flow directions in a continuous process. While reactor shape influenced reflection of ultrasound within the reactor, this was not a major factor in determining overall reactor performance. In fact, odd shapes led to lower volumes, higher dilution, shorter residence times, exhibited lower buffering capacity and were difficult to construct and maintain. The calorimetric energy efficiency increased with reactor volume in the order cylindrical > pyramidal > double cone > conical under both batch and flow conditions. The overall performance followed a similar order, cylindrical > double cone > pyramidal > conical, except that the double cone reactor slightly outperformed the pyramidal reactor under batch and flow conditions irrespective of flow direction.