The fundamental objective of this Geos 3 investigation was to determine the accuracy with which the local ocean geoid structure, expressed in terms of geoid undulations and vertical deflections, could be determined using satellite altimetry data. The approach taken to meet this objective was to estimate the undulation and the along-track component of the vertical deflection for selected passes of Geos 3 near the Blake Escarpment and to compare these results with independent analogous estimates based on U.S. Navy surface gravimetric survey data. The results of these comparisons show agreement in the geoid undulation values generally to within 1 or 2 m. The nature of the discrepancy in the undulation values was primarily that of a bias error believed to be due essentially to radial orbit uncertainties. The agreement between the vertical deflection estimates was not significantly affected by orbit uncertainties over the track lengths considered in this study (1000--1500 km), and the comparisons show typical rms differences of between 1 and 2 arc sec. An additional objective of this study was to determine the capability of the altimeter to resolve short-wavelength features of the geoid. This analysis involved spectrum and cross-spectrum analysis of sets of closely spaced parallel subtracks to determine statistically significant short-wavelength geoid resolution capability. The results of this analysis show that resolution can be achieved down to wavelengths as short as 30--80 km, depending on regional geoid variations.