The SOI/MDI experiment on SOHO has some unique capabilities for time-distance helioseismology. The great stability of the images observed without benefit of an intervening atmosphere is quite striking. It has made it possible for us to detect the time of flight for separations of points as small as 2.4 Mm in the high-resolution mode of MDI (0.6 arcsec/pixel). This has enabled us to detect the supergranulation flow beneath the surface. Using a tomographic inversion technique, we can now study the 3-dimensional evolution of the flows near the solar surface.