The onshore Sirt Basin, Libya, has yielded some of the world’s largest petroleum discoveries. The offshore extent, however, is poorly constrained. Recent wells have proven both equivalent and new petroleum systems in the offshore, but the extent, character and full potential of these systems is currently poorly understood. Furthermore, the structural complexities of the offshore area and the relationships between the ancient crustal domains are only starting to be realized. We place the offshore Sirt Basin and Cyrenaica Margin into a regional context and demonstrate the relationship with the onshore basins to define the huge play potential of this underexplored province. This mega-regional basin study has used over 45,000 km of recently acquired and depth processed deep regional seismic data and newly reimaged legacy 2D seismic data has been interpreted and integrated with offshore well data.