The data set comprises of geophysical observations in the source regions of the 2004 and 2005 great Sumatra earthquakes. Geophysical surveys were carried out to determine the seabed bathymetry and underlying structure and geometry and included the collection of seismic reflection, magnetic, gravity, and sidescan sonar data. In addition, Conductivity-Temperature-Depth (CTD) and Sound-Velocity Probe (SVP) data were collected, as well as continuous meteorological (air pressure, air temperature, radiance, relative humidity, wind direction and speed) and sea surface (temperature and conductivity) data. Data were collected in the Indian Ocean, west and north west of Sumatra between 8 degrees South, 6 degrees North, 94 and 108 degrees East. The data were collected during three cruises, SO198-1, SO198-2 and SO200 over two legs SO200-1 and SO200-2. The three cruises took place between May 2008 and February 2009. The data collection focussed on the areas around two earthquake segment boundaries: Segment Boundary 1 (SB1) between the 2004 and 2005 ruptures at Simeulue Island, and Segment Boundary 2 (SB2) between the 2005 and smaller 1935 ruptures between Nias and the Batu Islands. Measurements were taken using a variety of instrumentation across all three cruises including: the long-term deployment of 50 Ocean-Bottom Seismometers (OBS) deployed on cruise SO198-1 and retrieved on cruise SO200-1; 154 Expendable Bathythermograph (XBT) probes; high resolution multichannel seismic reflection (MCS) profilers; Swath bathymetric and backscatter echosounders; SVPs and CTDs which were deployed simultaneously; and a gravity meter and Parasound sub-bottom profiler were operated continuously within the survey areas. In addition, sea surface and meteorological measurements were made using the underway system throughout the three cruises, although there are no data for days at the beginning and end of the cruises of up to 10 days. During the two legs of SO200 additional instrumentation was deployed including: a 30 kHz deep-towed sidescan sonar system (TOBI); piston cores and megacores collected along the plate margin; and heatflow probes long transects. The UK Sumatra Consortium project aimed to characterise the subduction boundary between the Indian-Australian plate and the Burman and Sumatra blocks (including subduction zone structure and rock physical properties), record seismic activity, improve and link earthquake slip distribution to the structure of the subduction zone and to determine the sedimentological record of great earthquakes (both recent and historic) along this part of the plate margin. The project will allow better assessment of future earthquake magnitudes and locations, and further the general understanding of the earthquake rupture process. The UK Sumatra Consortium project was led by the National Oceanography Centre Southampton (NOCS) and involved five UK partners; NOCS, the universities of Cambridge, Oxford and Liverpool, and the British Geological Survey as well as numerous international partners including French, German, American, Indonesian and Indian Collaborators. The principal investigator was Dr Timothy Henstock from NOC. The Natural Environment Research Council (NERC) funded data will be managed by the British Oceanographic Data Centre (BODC).