Sustained oscillations occur under batch, semibatch, or flow (CSTR) conditions at the surface of a Pt electrode immersed in solutions at pH <2 containing Mn(III), Mn(IV), or Mn(VII) and H2PO2-. Additives such as F- and PO43-, which stabilize Mn(III) and Mn(IV) species, lengthen the duration of the batch oscillations. Measurements of the reaction rates of the Mn species with H2PO2, the similarity in the character of the oscillations, and other observations suggest that Mn(III) plays a key role in maintaining the oscillations. This phenomenon, which may be thought of as an open circuit electrochemical oscillation, represents the first example of an electrochemical oscillator based on manganese chemistry.