Periodic oscillations in both pH and the potential of a platinum electrode have been observed in the H2O2Na2SO3-Na2CO3-H2SO4 system using a continuous-flow stirred tank reactor. This homogeneous system was studied at 25 degrees C over a wide range of concentrations and flow rates. Phase diagrams delineating the behavior of the system under various conditions have been obtained. The main features of the experimental results have been duplicated by a computer simulation based on a proposed model. Positive feedback in H+ is provided mainly by the autocatalytic oxidation of HSO3- by H2O2. The main process for negative feedback in H+ is the dehydration of H2CO3 to CO2. Simulations predict a period-doubling route to chaos, which is also suggested by experimental results. The effects of carbonate and acid impurities in the Na2SO3 source and of atmospheric CO2 are both simulated and discussed.