The Rub' al Khali Basin (ٱلرُّبْع ٱلْخَالِي) or ar-Rubʻ al-Khālī / ar-rubʿ al-ḵālī Basin, Arabic for "Empty Quarter Basin", is a major endorheic sedimentary basin of approximately 560,000 square kilometres (220,000 sq mi) in southern Saudi Arabia, northeastern Yemen, southeastern Oman and southeasternmost United Arab Emirates. The onshore foreland on Mesozoic rift basin is geographically defined by the eponymous Rub' al Khali and covers the regions of Najran and Riyadh and the Eastern Province. The basin is geologically bound by the in the north, the in the east, the in the south and the Arabian Shield in the west. Politically, the southwestern boundary is formed by the border with Yemen and the border with Oman forms the southeastern boundary.