The results of an extensive literature survey of previous geological and geophysical research into the south-vest Scotia Sea are presented. Techniques used in the data processing of over 80 marine magnetic traverses steamed between 1964 and the present day in the Bransfield Strait area are described. Qualitative interpretations of the bathymetry, the regional magnetic field and two seismic reflection profiles are presented. Fourteen magnetic anomaly profiles have been modelled in order to determine the nature of the evolution of this area, while two graYity models are presented as confirmation of the crustal structure of Bransfield Strait. The results from the magnetic modelling indicate that stripes of normal and reversed polarity cruet exist in Bransfield Trough. It is likely that this crust has been generated by a process of sea-floor spreading during normal and reversed epochs of the Earth's magnetic field. Although the width of generated crust in the trough varies, an average of 32 km has been produced over the last 1.3 m.y. at a mean spreading rate of 24 mm yr -1. A line of seamounts represent a spreading centre which may be offset by five transform faults. Sea-floor spreading here appears to be disordered, and intermittent ridge activity during extension reflects the immaturity of the system. Volcanic and earthquake evidence indicate that Bransfield Strait is still actively undergoing extension at the present day.