Medium-wavelength (1000--4000 km) geoid and depth anomalies are positively correlated over a number of oceanic features. We have computed the geoid to topography ratio (or admittance) over 28 areas covering midplate swells, seep-sea troughs, and aseismic plateaus after correcting the data for lithospheric cooling effects and for sediment loading. The observed admittances range from ~1 to ~5 m km-1 depending upon the area considered. Aseismic plateaus have a low admittance, consistent with Airy compensation by crustal thicknening. Larger admittances are observed above mid-ocean swells and ocean deeps. For these latter features a linearly increasing trend with the square root of plate age of is observed. Linear regression indicates an admittance increase of 0.53 m km-1 per (m.y.)1/2. Observed admittances are consistent with dynamic support by convective upwellings and downwellings, provided that a shallow, low-viscosity layer exists beneath the lithosphere. According to recent convection modeling, the observed admittance increase with age may be understood either in terms of viscosity increase of the low-viscosity layer, from ~10-2 at mid-ocean ridges to ~1 in old basins (mean upper mantle viscosity taken as reference) or in terms of thickness increase of the lithosphere at the expense of a low-viscosity layer of constant viscosity. ¿ American Geophysical Union 1988