The Rub' al Khali[note 1] (/ˈrʊb æl ˈkɑːli/;[1] Arabic: ٱلرُّبْع ٱلْخَالِي, [ar.rʊbʕ‿al.χaːliː]) or Empty Quarter is a desert[2] encompassing most of the southern third of the Arabian Peninsula.

[6]: 213 Along the middle length of the desert, there are several raised, hardened areas of calcium carbonate, gypsum, marl, or clay that were once the site of shallow lakes.

The lakes are thought to have formed as a result of "cataclysmic rainfall" similar to present-day monsoon rains and most probably lasted for only a few years.

[3] The region is classified as "hyper-arid", with annual precipitation generally less than 50 millimetres (2.0 in), and daily mean relative humidity of about 52% in January and 15% in June–July.

South Ghawar, discovered in 1948, is the largest oil field in the world and extends southward into the northernmost parts of the Empty Quarter.

Between 1946 and 1950, Wilfred Thesiger crossed the area several times and mapped large parts of the Empty Quarter including the mountains of Oman, as described in his 1959 book Arabian Sands.

[17][6] In June 1950, a US Air Force expedition crossed the Rub' al Khali from Dhahran, Saudi Arabia, to central Yemen and back[18] in trucks to collect specimens for the Smithsonian Institution and to test desert survival procedures.

[21] In February 2013, a South African team including Alex Harris, Marco Broccardo, and David Joyce became the first people to cross the border close to Oman of the Empty Quarter unsupported and on foot,[22] in a journey which started in Salalah and lasted 40 days, ending in Dubai.

The team only made use of three water stops along the journey and pulled a specially designed cart that housed all the supplies necessary for the entire expedition.

[24] In 2013, from 18 February to 28 March, South Korean explorer Young-Ho Nam led a team (Agustin Arroyo Bezanilla, Si-Woo Lee) on a crossing through the Empty Quarter on foot from Salalah, Oman, to Liwa Oasis in the UAE Emirate of Abu Dhabi.

Dewan Ruler's Representative for Western Region, Emirate of Abu Dhabi recognized it as the world's first on-foot crossing of the Empty Quarter following the border of Oman and ending in UAE.

[25] In 2018, the first all-female walking expedition named "her faces of change" led by Briton Janey McGill who was accompanied by the first Omani women in modern times to walk the Oman Empty Quarter, Baida Al Zadjali and Atheer Al Sabri, set off on 22 December 2018 after receiving formal approval from the government of Oman.

[26] The team was supported by two cars for supplies driven by Tariq Al Zadjali (Omani) and Mark Vause-Jones (British) and filmmaker Matthew Milan from the United States.

The route was planned by Austrian Thomas Brandl-Ruttner, leading a team of eight experts in navigation, expedition logistics, and engineering.

[30] In 2024, Richard Midwinter walked alone from Salalah, aiming to cross via Muqshin to Al Ain and on to Dubai, to raise awareness for women missed by the NHS breast cancer screening programme.