This EPP 26 surrender report has been furnished to the SA offshore Designated Authority as a result of the application made on 21/8/96 by BHP Petroleum for permission for the joint venture to surrender the permit, before committing to unwanted mandatory additional drilling expenditure in permit Year 6 (1996-1997). In the report the joint venture's concepts of Duntroon Basin and Eucla Basin petroleum prospectivity within the EPP 26 area are discussed in general terms based on stratigraphic, structural, drillhole geochemical sample analysis and seismic geophysical mapping information gained during their tenure. An overview is given of the sedimentology of the three major stratigraphic subdivisions present in the basins, of their regional tectonostratigraphic geochronology, of the present structural geology interpreted in the context of pre-existing structural grain, normal passive continental margin development processes and extra-basin tectonic events, plus of drilling results from Platypus 1, Greenly 1 and Duntroon 1 including brief assessments of sedimentary unit hydrocarbon potential based on source, reservoir and seal properties determined from well logging, testing and sampling. In common with other, proven hydrocarbon-bearing sedimentary basins along the southern Australian continental margin, the EPP 26 main target, the Duntroon Basin, has resulted from the separation of the Australian and Antarctic continents. Structurally, it is subdivided into an Early Cretaceous Inner Sub-basin and a Late Cretaceous Outer Sub-basin, separated by a Late Cretaceous hinge zone. The basin fill consists of the syn-rift, Late Jurassic to Early Cretaceous Duntroon Group megasequence, comprising fluvial to lacustrine to lower coastal plain sediments with some shallow marine interdigitation; the early post-rift phase, Cenomanian to Eocene Bight Group megasequence, comprising marine, progradational, coarse and fine-grained clastics; and the latest post-rift, Miocene to Holocene Eucla Group megasequence of prograding, carbonate-dominated sediments. The petroleum potential of the basin's source rocks is related both to their lithotype and depositional location, with source quality generally appearing to improve basinward. Interpreted reservoir and seal unit properties show that porosity degrades fairly uniformly with depth, but consistent with changes in facies and provenance: an anomalous acid volcanic detrital input from the Otway Basin during the Upper Albian is also discussed in this regard.