Geosat altimetry is well suited for locating large eddies shed by the Loop Current in the Gulf of Mexico. We have compared the altimeter data with in situ data obtained during a survey of Eddy Murphy in June 1988. Since there is no significant mean circulation in the central gulf, we used the mean sea surface from the first year of altimeter data as a geoid estimate. The dynamic height change due to the eddy closely matched the altimeter data, although the eddy moved about one third of a degree between the survey and the satellite pass. The motion of the eddy was confirmed by the track of an Argos buoy.