Passive continental margins are a key terrane worldwide for the exploration and production of hydrocarbons. New models for the formation of passive margins have been proposed invoking variable large extensional displacements on low-angle fault systems and depth dependent stretching of continental crust until eventual breakup and crustal separation. New high quality 3D seismic data combined with new 2D data and legacy regional seismic sections across the Australian Northwest Shelf passive margin as well as along the southern Australian margin have been used to determine the role of low-angle fault systems in these terranes. New interpretations of these areas are presented and compared with recent results obtained from the South China Sea. Our studies have shown that extremely low angle faults commonly occur on these margins and in places these may evolve to extreme deformation and the formation of metamorphic core complexes. Extreme crustal thinning in these settings also may lead to significant magma emplacement in the footwalls of these low-angle faults systems. The models developed from this research and their implications for hydrocarbon systems are compared to other passive margins such as the Norwegian North Atlantic margin as well as metamorphic core complex terranes in the western USA, Greece and Turkey.