We study the resistivity index of Fontainebleau and Bentheimer sandstones at ambient conditions down to low water saturations both experimentally and numerically. Numerical simulations are in good agreement with experimental measurements of capillary drainage resistivity index by the porous plate method down to water saturations as low as S (w) = 10 %. Fontainebleau sandstone exhibits a percolating network of grain contacts, while the higher porosity Bentheimer sandstone does not. We show that this difference in the topological connection of conductive films at low water saturations is responsible for the non-Archie behaviour of Fontainebleau sandstone. Furthermore, it is necessary to attribute a grain contact conductivity to the grain contacts in Fontainebleau sandstone to reconcile experiment and numerical simulation. Conductive films organised as pendular rings around grain contacts are not able to explain this result.