AIM:The Della Field of the southern Cooper Basin was covered by sparse poor quality seismic data until 1977, when the first Vibroseis (digitally acquired) work was done over the area. The lines recorded in 1977 tied the field to the Vibroseis grid progressively being extended throughout the southern Cooper Basin, but did not cover the field in any detail. The 1978 Della Development Seismic Survey was designed to detail the field prior to development drilling, and to establish a closely-controlled (1800m maximum grid spacing) structural model for the optimum locating of development wells.METHODS: Survey dates: 16/10/78 - 7/11/78. Energy source: Vibroseis. CDP coverage: 1200%. Recording mode: 48 channel digital - Sum-it VII recorder. SP/VP interval: 150.0 metres, group interval: 75.0 metres.9 E-W and N-S orientated lines totalling 84 line km of reflection seismic data, and passing through all 6 existing exploratory wells, were acquired by Geosource Inc., and processed in Sydney by GSI.RESULTS:The Della Development Seismic Survey has confirmed three general features of the Della Field structure recognized from the 1977 mapping of the P-Horizon. These are: a) that the field closure is divided into two culminations, with the Della 4 area separated from the Della 5A culmination; b) that the centre of the eastern culmination, previously mapped near Della 1, has been shifted northwards and enhanced in relief; c) that a postulated culmination NE of Della 3 could not be confirmed, but was shown to be a nose associated with the western flank of the Nappacoongee feature. From the latest, digital data, the saddle between the two field culminations has been proven by line 78-JQG. A small, third culmination is also postulated NW of Della 5A, but the present seismic coverage is insufficient to confirm its existence at P level. The 1978 survey final report presents eight field interpreted reflecting horizon cross-sections in both time and depth versions. The depth structural views show the stratigraphic relationships of the principal mapped horizons, and the P-Horizon datumed seismic profiles highlight the depositional and erosional history of the field. Attempts were made to identify the field gas-water contact directly on the seismic data, but little evidence of an identifiable seismic response was seen. This was not altogether unexpected, since the well sonic logs did not reveal a persistent velocity contrast at the contact intersections.