Rub al Khali (rōb äl khäˈlē) [key] [Arab., = empty quarter], great desert of the Arabian peninsula, c.225,000 sq mi (582,750 sq km); one of the largest sand deserts in the world. The desert occupies much of the southern interior of the peninsula, from the highlands of the Nejd (to the north) to the plateaus of Hadhramaut (to the south); it slopes from an altitude of 3,300 ft (1,006 m) in the west to near sea level in the east. Sand dunes rise to over 660 ft (200 m) in the southwest; there are salt marshes and pans in the southeast. Rub al Khali is connected to the Nafud desert in the north by the Dahna, a narrow corridor, 800 mi (1,287 km) long. The desert comprises more than 25% of Saudi Arabia. It is extremely dry and virtually uninhabited. Oil of excellent quality has been found there and is exploited. The al-Ghawar oil field is one of the world's largest.