AIM:The 1981 Rainbow Plains Seismic Survey semi-detailed programme was designed by the PELs 5 and 6 Birdsville Track Ridge Block partners to further define the Haddon Downs structural feature, which in 1979 had been identified on regional line 79-QAM by the 6-fold Pulcara Seismic Survey as a narrow, anticlinal dome with a nearly N-S trend, separated into northern and southern culminations by a saddle.METHODS: Survey dates: 6/5 - 7/6/81 and 12/8 - 3/9/81. Energy source: Explosive line source (Geoflex). CDP coverage: 1200%. Recording mode: 48 channel digital - Texas Instruments DFS V recorder. SP interval: 150.0 m; group interval: 75.0 m.RESULTS:12 lines totalling 218 line km of semi-detailed reflection coverage were shot and recorded by Geophysical Exploration Service's Party 1, and processed in Singapore by Western Geophysical Company. Data interpretation performed by operator Delhi Petroleum resulted in the mapping of four marker horizons thought to represent events extending from the top Transition Beds through to the top of the pre-Triassic basement. The Rainbow Plains survey has provided additional seismic data to allow improved mapping of the Haddon Downs dome, which is now seen to have an areal closure of approximately 100 square km. Several other significant rollovers were also delineated, including a steeply dipping one on line 81-QJL, and two on line 81-QJP. No Cooper Basin sedimentary section has been mapped over the Haddon Downs area, with the Permian strata zero edge subcropping slightly to the southeast of the survey grid, beyond the end of line 81-QJP.Major NE-SW faults with secondary orthogonal faults are characteristic of all the anticlinal features mapped. The Haddon Downs anticline is fault-bounded on the west and northeast, with a gentler dip to the east. A preliminary well location was picked at SP 240 on line 81-QJM, at the structural crest of the Haddon Downs southern lead.