Voltammetric studies of hydrogen gas evolution from 1 M H2SO4 and chloride gas evolution from 2.5 M NaCl/0.1M HCl both at platinised platinum electrodes show that simultaneous ultrasonic irradiation produces enhanced rates of gas evolution largely due to the removal from the electrode surface of adherent product species. Nitrogen-agitation is less efficient at promoting this product removal. In contrast, oxygen gas evolution from the same electrode in 1M H2SO4 not only fails to be enhanced by ultrasound in these conditions, but the electrode continues to be deactivated by oxidative processes on successive scans despite sonication. Thus sonoelectrochemistry probes mechanistic distinction between these reaction systems.