AIM: A high resolution, digital marine seismic reflection survey, and secondary bathymetry and side-scan sonar surveys plus drop coring of sea floor sediments, were carried out for EPP 25 operator BHP Petroleum Pty Ltd during March 1993 over a 3 km square area centred on the proposed Vivonne 1 offshore drilling location. The purpose of this site survey was to check the sea floor for suitable drilling rig anchoring conditions, and to identify potential local drilling hazards, e.g. near-seabed shallow gas accumulations, occurring in the uppermost continental shelf section, particularly down to the 20 inch casing point at 440 metres depth subsea. METHODS: Survey dates: 18/3/93 - 24/3/93. Energy source: Airgun. Recording mode: 96 channel digital - Titan 1000 recorder. SP interval: 6.25 metres, group interval: 6.25 metres. 52 line km of digital data and 114 km of analogue data were respectively acquired by contractors Halliburton Geophysical Services and Racal Survey Australia, using the M/V 'Pacific Titan' working out of Port Lincoln, and the digital data was processed in Perth, WA, by Simon Petroleum Technology. Operator BHP performed the geophysical interpretation of the survey results. RESULTS: One significant drilling constraint was noted at the proposed Vivonne 1 location. Drilling is expected to encounter a channel with possible gas sands at 208 metres SS. Gas charge is suggested by the pushdown underlying the channel and degradation of the stack. At this stratigraphic level minor closures with marked amplitude anomalies at the crest exist approximately 350 metres to the west and 250 metres to the south of the proposed location. The main controlling fault is intersected at 566 metres SS. Caution is advised when approaching these levels.