Rifting between Australia and Antarctic began as early as 140 MM years ago. However, the timing of continental breakup and the manner in which rifting proceeded have remained controversial. A major reason for the ambiguity surrounding the Australian- Antarctic breakup and early spreading history is the lack of a clear boundary between continental and oceanic crust. Instead of a sharp boundary there is a zone of transitional crust, up to 120 km in width, along the entire conjugate southern Australian and east Antarctic margins (Sayers et al. 2001). The presence of wide zones of so-called transitional crustal on conjugate rifted Australian- Antarctic margins have resulted in considerable scientifi c debate regarding the nature of the transitional crust. Here we assess the ability of available data to discriminate between different hypotheses regarding the nature of the crust of the Australian- Antarctic conjugate transition zones. We also assess the suitability of applying depth-dependent rifting models recently developed for the well-studied Iberian-Newfoundland conjugate margins to the Australian-Antarctic context in order to resolve the nature of the transitional crust and the manner in which it formed.