A test aerial spectrometric and subsidiary aeromagnetic survey of the onshore Otway Basin in SA was proposed in 1991 by APIRA, the Commonwealth Government's petroleum research authority. Initially it was aimed at utilising possible signature responses over three proven petroleum fields, Katnook, Ladbroke Grove and Caroline, to identify further accumulations, and was later expanded in scope to address the whole basin area. The proposal languished for want of unilateral industry support until September 1993, when with redefined objectives and limited company participation MESA acquired the P1 aeromagnetic (principally) / aerial radiometric survey over only some of the onshore basin as part of the South Australian Exploration Initiative. The P1 survey was flown mainly over the northern margin of the Otway Basin, the Penola Trough, the Kalangadoo High and the eastern margin of the Tantanoola Trough, plus across a contiguous southern area covering the Tartwaup Hinge Zone where Tertiary and Upper Cretaceous sediments thicken rapidly to the south. A total of 11 834 line km of new geophysical data were recorded at 400 metre line spacing and 80 metre flight height, funded in part by licence holders in the test areas. Sediment thicknesses derived from a composite regional seismic line and magnetic susceptibility measurements taken from petroleum well cores and basaltic outcrops were used to model magnetic responses. The volcanic vents at Mount Gambier and Mount Schank were modelled, as well as a blind intrusive plug to the north near the Hungerford 1 well. The total magnetic intensity response was pseudo-depth sliced using frequency increments, into four slices in the sedimentary section and a fifth basement slice. These pseudo-depth slices were then compared to MESA seismic depth structure maps of the section extending from top Cretaceous to top basement (i.e. fault patterns were compared to magnetic lineaments). A sidescan radar image was used to identify surface culture (towns, railway lines, sheds, etc.) that cause high frequency anomalies in the TMI data. A map of the powerline grid in the area was obtained from ETSA and the grid was digitised and displayed at the same scale as the aeromagnetic data to identify powerline cultural anomalies.