It is bordered on the W by the Gulf of Aqaba and the Red Sea, on the S by the Gulf of Aden and the Arabian Sea, on the E by the Gulf of Oman and the Persian Gulf, and on the N by Iraq and Jordan. Except for the inland cities of Riyadh and Hail, in Saudi Arabia, most of Arabia's large urban centers are on or near the coast. Geography and Climate Arabia is mainly a great plateau of ancient crystalline rock, largely covered with limestone and sandstone. The northeast coast of Oman has a climate similar to that of Yemen, but in most of Arabia rainfall occurs only in winter.
Desalination plants supply much of the population's drinking needs.
Osmosis distillation processes take brackish underground water and make it useful for agriculture and industry. With the exception of Aden, Arabia did not have a good port until after World War II, when modern port facilities were constructed, especially along the Persian Gulf. Arabia has the largest oil reserves in the world, in addition to great amounts of natural gas. Saudi Arabia is the world's leading exporter of oil. Until the early 1970s, oil firms from the United States, Britain, and to a lesser extent Japan, had a monopoly on drilling concessions.