From May 1975 to October 1978 the GEOS 3 satellite altimeter made numerous repeated observations of sea surface topography in the northwest Atlantic and Gulf of Mexico. By comparing members of about 1000 collinear pairs of altimeter profiles, we have determined mesoscale sea height variability and eddy kinetic energy in these ocean regions. Our results agree qualitatively with estimates made from traditional oceanographic surveys, but significant quantitative differences exist in certain areas, especially in the Gulf Steam between Florida and Cape Hatteras where the alimetric results show less variability. The reason for this appears to be due to differences in spatial sampling. Historical oceanographic measurements are relatively sparse and must be aggregated into small geographic boxes to compute variability statistics. Results therefore represent a combination of temporal and spatial variability. In contrast, repeated satellite altimeter tracks provide point measurements of changes of sea height and slope. This enables determination of temporal variability alone, a quantity more representative of eddy slope. It is important to make this distinction between space and time because in regions of strong horizontal gradient such as the Gulf Stream, spatial variability can exceed the temporal component. In mid-ocean where spatial variability is negligible, altimetric and oceanographic results are in excellent agreement.