AIM: This detailed seismic survey of 12 lines totalling 90.2 line km was proposed to define an optimum location on the Katnook Structure at which to locate an appraisal well for further drilling evaluation of the Katnook gas discovery. In addition to evaluating the Cretaceous Eumeralla Formation gas reservoir structure, the seismic work would also be focussed on identifying possible deeper drilling targets in the area. Accordingly, field tests were conducted by the contractor GSI to modify the previous survey acquisition parameters to achieve both these purposes. METHODS: Survey dates: 5 - 19 May 1988. Energy source: Vibroseis. CDP coverage: 6000%. Recording mode: 120 channel digital - DFS-V/FT-1/RTC recorder. SP interval: 25.0 m; group interval: 25.0 m. The twelve 1988 lines, plus four lines of concurrently reprocessed 1986 and 1987 data (lines 86-141, 86-153, 87-151 and 87-184a), were incorporated into the update of the previously completed regional seismic mapping. Seven reflector horizons were picked, of which 3 were immediately mapped for inclusion in the survey interpretation to allow selection of a drilling location. RESULTS: The 1988 Penola Seismic Survey has confirmed the size and shape of the Katnook gas reservoir pay structure at the top basal Eumeralla Formation level. It is a NW-SE trending closure of approximately 15 milliseconds (ms) relief. 2 separate culminations exist at this level, with the NE one being slightly higher. A second closure exists to the east. At the deeper Banyula Sandstone level the structure is much less complex, being a simple NW-SE trending anticlinal closure formed on the downthrown side of a major listric fault. Over 90 ms of closure is present. In addition, this survey has further delineated the Ladbroke Grove Structure lying on the upthrown block of a major fault which bounds the Katnook Structure to the south. The structure is closed against the fault at both objective horizons, with 65 ms closure on several separate culminations at the top Eumeralla 'pay' horizon, plus at least 165 ms closure at top Banyula Sandstone. The survey was successful in revealing on Katnook prospect an updip location for an appraisal well at VP 224 on line 88-022, which also embraces a secondary, deeper target . Field testing of line 87-153 running through Katnook 1 has indicated that longer spread lengths do improve the definition of deeper horizons. Consideration should be given to increasing the numbers of channels to enable the use of larger symmetric spread configurations in future surveys in the area. Processing tests suggest that improvements in data quality can be effected by applying DMO (dip move-out) and Tau-P techniques. Use of these processes should be continued.