Particle in cell plasma simulation technique has been used to study the effect of the ion two-stream instability on hydrogen and oxygen distributions at small relative drifts (&ngr;H+-&ngr;O+<2cH, the hydrogen sound speed). We investigate whether heating due to parallel modes which are unstable at low drifts might be sufficient to quench oblique modes which are unstable at higher drifts. We find that this is not the case and that the oblique modes contribute significantly to heating. ¿American Geophysical Union 1990