Persian Gulf, an arm of the Indian ocean, between Persia and Arabia, extending mainly from lat. 24° to 30° N., and from Ion. 48° to 56° 30' E.; extreme length 550 m., breadth from 40 to 250 m.; area estimated at about 80,000 sq. m. Its entrance from the Indian ocean is through the Arabian sea, the gulf of Oman, and the strait of Ormuz, the last of which is about 35 m. wide. The shores are much indented; but the only harbor of importance is Bushire, besides Bassorah on the Shat-el-Arab. The coasts are low, except near the entrance, where the mountains on both sides rise to a considerable height and come close to the sea. On the S. W. or Arabian side there are numerous shoals and reefs. There are several islands in the neighborhood of the Arabian shore and the strait of Ormuz, the most important of which are Kishm, Ormuz, and the Bahrein or Aval islands. The only considerable river that falls into the gulf is the Shat-el-Arab, or the united stream of the Euphrates and Tigris. At the straits of Ormuz the tide rises 12 ft., and about the N. end of the gulf 6 ft.

There are valuable pearl fisheries in the neighborhood of the W. and S. shores. - The shores of the Persian gulf are inhabited almost exclusively by Arabs. For many years the gulf was infested by pirates, who found safety among the shoals and islands on the coast of Arabia. In 1809, and again in 1819, the British sent expeditions against them from Bombay, which, in conjunction with the imam of Muscat's forces, completely destroyed their vessels. The Persian gulf is the ancient sea of Babylon, and the earliest record (besides the Scriptural accounts) which we have of its navigation is that of the voyage of Nearchus in 325 B. C.