AIM: The permit Year 3 Rhonda 'B' seismic programme in EPP 23 was designed to identify a target for drilling with the permit Year 4 commitment well, preferably addressing a play type different to that tested by the unsuccessful Copa 1 (the permit Year 2 well). A large prospect at the edge of the continental shelf, 55 km southeast of Copa 1 and and 10 km south of Argonaut A 1, had been identified and mapped on reprocessed and redisplayed 1988 seismic lines. This structure had been named the Ipanema Prospect. Approximately 100 km of the lines in the current survey were programmed to fully define this prospect. The failure of Copa 1 to discover significant hydrocarbons, and the success onshore of the Katnook and Ladbroke Grove wells, have directed the exploration effort in EPP 23 towards the Early Cretaceous sediments. The northern portion of EPP 23 (Crayfish Platform) has a thick section of shallow Early Cretacous sediments covering an area of approximately 500 square km. Previous seismic mapping in the area had identified 3 Pretty Hill Formation leads, and the remaining 200 km of new seismic acquisition was aimed at better definition of these leads. METHODS: Survey dates: 28/7/90 - 3/8/90. Energy source: Air gun. CDP coverage: 7500%. Recording mode: 300 channel digital - Titan 1000 recording system (DFOS, SCS and FCS III). SP interval: 25.0 metres; group interval: 12.5 metres. 16 lines totalling 300.55 line km were shot in the two areas described above, by GSI using the M/V 'Pacific Titan', and later processed in Brisbane by Digicon. Interpretation of the survey results was done in conjunction with that of the rescheduled permit Year 4 OH91 marine seismic survey, also run over the same targets to more adequately firm up a drilling objective. RESULTS: Ipanema is the culmination at base Tertiary level of a large anticlinal structure formed during the Upper Cretaceous, and is dissected by a series of listric faults trending in a NW to SE direction parallel to the strike of the structure and the present-day continental shelf edge. These faults are expected to provide conduits for oil migration from deeper source rocks. Two types of reservoir are predicted: 1. Base Tertiary turbidite sands associated with progradational sequences; 2. Upper Cretaceous paralic sands. Further interpretation of Lower Cretaceous leads in the north of the permit is incomplete pending additional detailed seismic coverage in 1991. Presently there are 4 mapped leads (Socrates, Dundee, Pearl and lead 'D') having suspect viability both in terms of overall size and of seal integrity.