Geologically, the Rub' al Khali is the most oil-rich site in the world. Vast oil reserves have been discovered underneath the sand dunes. Sheyba, at the northeastern edge of the Rub' al Khali, is a major light crude oil-producing site in Saudi Arabia. Ghawar, the largest oil field in the world, extends southward into the northernmost parts of the Empty Quarter.For thousands of years this territory has resisted settlement as one of the Earth's hottest, driest, and most unyielding environments. Yet it's also home to a culture on the edge, a proud Bedouin society working to adapt its mix of Islam, ancient tribal custom, and newfound oil riches to a demanding and fast-paced modern world. Taking up a fifth of the Arabian Peninsula, the Rub al Khali (literally, "quarter of emptiness"), or the Sands for short, is the world's largest sand sea. At more than 225,000 square miles (583,000 square kilometers), it takes in substantial portions of Saudi Arabia, as well as parts of Oman, Yemen, and the United Arab Emirates to create an arid wilderness larger than France. It holds roughly half as much sand as the Sahara, which is 15 times the Empty Quarter's size but composed mostly of graveled plains and rocky outcrops. Because of these sandy expanses, not to mention its profound heat, the Sands have long been judged too unforgiving for all but the most resourceful humans, considered more a wasteland to cross than a landscape to settle in. Still, along its edges—and venturing across it from time to time—the dozen tribes of leathery and enterprising Bedouin, also known (especially in Arabia) as Bedu, have survived here since before recorded time.