In physical oceanography the slope of the sea surface can be used to calculate a surface geostrophic velocity as a reference for the general circulation and its associated transports. Here we calculate a new mean sea surface (MSS) by combining oceanography, altimetry and gravity data. A first guess MSS is calculated from a dynamical ocean model into which measurements of temperature, salinity, property fluxes and tide gauges have been assimilated. The large scales of this surface are subsequently improved by adding information from satellite altimetry and a 'satellite only' geoid model like the CHAMP derived EIGEN-1S. The combination takes into account the different error structures of the three sources of data. Simultaneous we estimate large scale corrections for the respectively used geoid models. Comparing the corrections of different geoid models makes it possible to verify the improvement of 'satellite only' gravity models by the CHAMP mission.