Mean gravity profiles have been obtained from gravity fields constructed using Geosat Geodetic Mission altimeter data for a number of areas over mid-ocean ridges. The technique of averaging many profiles reduces the effects of along-axis variability and allows systematic changes as a function of spreading rate to be seen more clearly. For spreading rates larger than about 60--65 mm/yr, an axial gravity high is observed with an almost constant amplitude (~12 mgal) that narrows as the spreading rate increases. For spreading rates lower than this, an axial gravity low is observed whose amplitude decreases rapidly with spreading rate while the width reduces only slowly. The disappearance of a median valley occurs abruptly on any one ridge, but occurs at slightly different spreading rates on the Southeast Indian Ridge (68 mm/yr) and the Pacific-Antarctic Ridge (60 mm/yr). These observations are compared with the predictions of current models of mid-ocean ridge processes but are not fully explained by them. ¿ American Geophysical Union 1994