The objectives of this project were to establish the geometry and internal structure of open system pingos in Adventdalen, Svalbard using electrical resistivity tomography. A clear distinction can be made between the electrical properties of the pingos investigated, depending upon whether they are located either above (Innerhytte pingo) or below (Hytte and Longyear pingos) the maximum Holocene marine limit. The resistivity profile at Innerhytte pingo was characterised by high values of resistivity (10,000–30,000 Ω m), indicating either ice-rich frozen bedrock or a lens of massive ground ice. The electrical resistivity of Hytte and Longyear pingos, both developed within fine-grained, saline marine clays, is exceptionally low (predominantly <2,000 Ω m) for permanently frozen ground. This is inconsistent with the presence of a body of massive ground ice, and suggests that the internal structures of Longyear and Hytte pingos do not follow the classic model of a plano-convex pingo-core of massive injection ice. Instead, the internal structure of these landforms may be dominated by segregation ice and localised pockets of massive ice within a matrix of partially frozen, fine-grained marine muds. The high salinity of the pore waters and the fine-grained nature of the sediment cause high unfrozen pore water contents, even at temperatures well below 0°C, enabling electrolytic conduction and resulting in apparently anomalously low resistivity measurements. It is therefore concluded that electrical resistivity tomography must be interpreted with care when applied to the characterisation of permafrost in areas of saline marine sediments. Future field monitoring of permafrost landforms and laboratory testing of ice-rich sediments are recommended to improve geophysical interpretation of permanently frozen materials.