Electrical resistivity methods, either in vertical electrical sounding mode or lateral mapping mode, assess the resistivity distribution in the subsurface. Electrical resistivity tomography (ERT) has been successfully applied to image fluid-flow processes at various length scales and depths, mainly with electrodes deployed at the surface.A practical application of the ERT monitoring technique was demonstrated at the geological CO2 storage site in Ketzin (Germany), where time-lapse surface- downhole ERT measurements as well as cross- hole ERT measurements have been carried out during a CO2 injection experiment. In the frame of the multidisciplinary monitoring concept, a combination of surface-downhole(SD) geoelectric measurements was tested (Kiessling et al., 2010) with the objective to enlarge the near-wellbore area, and to address limitations of the individual survey techniques. The geoelectric measurements at the Ketzin site comprise the following survey types: 3D SD-ERT, 2D SD-ERT and Crosshole ERT.The present data publication is focused on the 3D SD- ERT data sets only. Users have the opportunity to assess SD -ERT data in two main steps: The raw field data (voltage and current time -series) and the preprocessed apparent resistivities. The raw field data can be used to apply own preprocessing procedures in order to determine apparent resistivities. Using the pre- processed apparent resistivities, it is possible to start right away into the resistivity inversion.