A mean sea surface map has been computed for the global ocean areas between 70¿N latitude and 62¿S latitude based upon the 70-day set of Seasat altimeter data recorded in 1978. A combination of regional crossover adjustment techniques and a global reference surface, using the best available geodetic parameters for Seasat, has formed the basis for the computation. The overall rms value of the crossover residuals in the open ocean areas was 13 cm after the adjustment. A contour map of the crossover residuals is very similar in nature to earlier contour maps of the collinear pass results for mesoscale variability. The mean sea surface is presented in the form of a global contour map, a 0.5¿¿0.5¿ grid, and a computer-illuminated image.