Clear signals of internal tide propagation are found at the semidiurnal M2 frequency in the eastern South Indian Ocean over the abyssal plain of the Indonesian Australian Basin. We find a spatially and temporally coherent internal tide with phase propagation estimated from satellite altimetry suggesting generation along the Indonesian Archipelago and the Australian North West Shelf east of 115¿E. A sinusoidal fit is used to estimate internal tide phase and amplitude along vertical cross sections from expendable bathythermograph (XBT) data along volunteer merchant shipping lines. It is likely tidal energy in the middle of the Indonesian Australian Basin is from both northern and southern source regions, and may sustain a second region of enhanced mixing for the Indonesian Throughflow.