Satellite altimetry data provided by GEOS 3, Seasat and currently Geosat have been successfully used to measure sea surface variability. The determination of the ocean variability has been accomplished through either examination of differences along collinear tracks or differences at points where tracks cross. In either case it is first necessary to remove the relatively large long-wavelength error that exists in the sea surface heights due to inaccuracies in the estimation of the satellite altitude from ground based tracking data. This long-wavelength altitude error has generally been an order of magnitude larger than the short-wavelength variability that is being sought. A number of techniques have been applied to eliminate the altitude error with the most common being a simple modeling of the orbit errors as a linear trend over the region of interest. The intent of this study is to quantify the effectiveness of useing a linear model of altitude error when attempting to estimate sea surface variability. Although there are many sources of altitude error, only the influence of gravity modeling errors will be considered here. This is justified since this is the dominant error source in the estimation of the satellite altitude from ground based data. Additionally, gravity model errors are the primary source of altitude errors with wavelengths shorter than once per revolution. Analyses are presented for the case of geosat and TOPEX altitude errors due to the expected modeling uncertainties of the GEM-L2 and GEM-T1 gravity fields. Results are given in terms of the rms of the crossovers after removing linear trends along track and minimizing the crossovers. It is found that for scales below 10,000 km, both gravity models are equally effective. Also, the higher altitude of TOPEX Provides for significantly better performance of the linear orbit error correction model. The results indicate that the current GEM-T1 model induces crossover discrepancies of less than 5 cm rms at scales up to 10,000 km. ¿ American Geophysical Union 1990