Integrated analysis of geophysical data can provide valuable information on reservoir properties upon which exploration, appraisal, and development decisions can be made. Here we derive a geophysical reservoir characterization workflow from quantitative interpretation of towed-streamer electromagnetic (EM) and dual-sensor seismic data. The workflow facilitates the reliable extraction of complementary information from two high-fidelity data sets. We demonstrate how the new workflow enables a robust and reliable integration of towed-streamer EM and seismic data with examples from data acquired in a complex geologic region of the North Sea where the heavy oil fields known as Bressay, Bentley, and Kraken (BBK) are located. The BBK discoveries pose several challenges to EM surveying. Airwave coupling in the relatively shallow ocean significantly complicates the reservoir signals. Further, the reservoirs are in close proximity to other high-resistivity features, such as shallow gas in the overburden, the regional Balder Tuff, and granite intrusions. Seismic imaging over these fields is also challenging due to the presence of injectites with steep and irregular geometries. Furthermore, the heavy oil charge means there is no direct hydrocarbon indication in the seismic data due to the low acoustic impedance contrast between the reservoir and surrounding shale.