During preparations of the deep Digital Geological Model (DGM), seismic travel time data have to be converted to depth data. The VELMOD regional velocity model has been developed for this purpose, using velocity data recorded in wells (sonic logs and time-depth relationships). The ‘layer cake’ approach has been applied for all lithostratigraphic units, with the exception of the Zechstein Group. Each new version of VELMOD includes various changes, such as a switch from analogue to digital, increased data density and more detail in the lithostratigraphic units.