An 18-day set of SEASAT altimeter data and precisely computed SEASAT ephemerides have been combined using accurate gridding techniques to compute global contour maps of the mean sea surface topography. The earth gravity models specially developed for SEASAT precision ephemeris computations (PGS-S3 and PGS-S4) have been used to calculate the ephemerides over this 18-day time period. The altimeter data have an rms agreement of 111 cm with the SS3 mean sea surface computed using the PGS-S3 ephemerides and 70 cm with the SS4 mean surface computed using the PGS-S4 ephemerides. Comparisons with the GEM 10B 1¿¿1¿ detailed gravimetric geoid have rms differences of 2.8 m, while comparisons with a global mean sea surface computed from GEOS 3 altimeter data have rms differences of 1.3 m for the SS3 surface and 1.1 m for the SS4 surface.