The distribution of oceanic and continental crust in the eastern Mediterranean region is not well understood but has major implications for tectonic evolution of this region and its petroleum systems. In particular the location of the continent-ocean boundary (COB), the ocean-continent transition (OCT) structure, and crustal thickness within the basin regions is a topic of much debate. While seismology, especially refraction seismology, is an ideal method for locally determining crustal thickness, it is limited to 2D as 3D mapping of crustal thickness is not practical or affordable over large areas. However, a recent development in 3D crustal thickness mapping uses gravity anomaly inversion. We illustrate the application of this technique using the example of the eastern Mediterranean (Figure 1). The new 3D gravity inversion technique, incorporating a lithosphere thermal gravity anomaly correction, is used to map Moho depth, crustal basement thickness, and continental lithosphere thinning. We then use this to determine the distribution of oceanic and continental crust, and ocean-continent transition structure, for the eastern Mediterranean.