Rates of mass transfer were measured at the inner surface of an annular duct by an electrochemical technique under developing flow conditions with superimposed pulsating flow. Variables like the frequency and amplitude of the pulsating flow, steady flow velocity, and annulus height were studied. The pulsating flow was found to enhance the rate of mass transfer by a factor ranging from 1.2 to 5.5 compared to the steady laminar flow value. The superimposed pulsating flow had only a minor effect on the rate of mass transfer under steady turbulent flow conditions. The pulsating flow reactor offers the advantage over steady flow annular reactor in that it can be operated at low flow rates to increase the residence time. The high residence time and high rate of mass transfer resulting from pulsation together increase the degree of conversion per pass as well as the reactor productivity.