Upolu (ōōpō´lōō), volcanic island (1986 est. pop. 163,000), Samoa, S Pacific, the most populous of the Samoan islands. Upolu's land area is c.430 sq mi (1,110 sq km); the highest peak is Vaaifetu (c.3,600 ft/1,100 m). The island is well watered, and its fertile soil yields cacao, rubber, bananas, and coconuts. Apia, the capital of Samoa, is the chief port and major city of the island. At Saluafata, the second port, there is a U.S. naval station. Robert Louis Stevenson spent his last years on Upolu, residing at his home, Vailima.