A passage just two miles wide

The oil-producing countries around the Persian Gulf, including Kuwait, Saudi Arabia, Iraq and Iran, are crucial for supplying the world oil market. Most of their exports, around 18 million barrels a day or about 20 percent of world demand, must travel through the Strait of Hormuz.

The strait, separating the United Arab Emirates, Oman and Iran, is 21 miles wide at its narrowest point, but the width of the shipping lane in either direction is only two miles wide, according to the United States Energy Information Administration. Dozens of ships a day move through the passage.

The bulk of this traffic heads for Asian markets like China, India and Japan. Large volumes of liquefied natural gas, an increasingly important fuel, follow the same route from the tiny emirate of Qatar.

But this area has been rocked by instability in recent weeks. In May, there were reports that four oil vessels were attacked near the Strait of Hormuz, heightening concerns over rising tensions between Iran and the United States. A day later, a drone strike on oil pipelines, claimed by Houthi rebels, forced the Saudis to suspend the flow of oil to the western side of the country.