All the oceans considered together are called the World Ocean. The World Ocean is divided by the continents into three major oceans—the Atlantic, the Pacific, and the Indian. The Atlantic lies to the east of North and South America, and the Pacific lies to the west. The Indian Ocean lies to the south of India, Pakistan, and Iran. Some scientists consider the water surrounding the North Pole as a fourth ocean, the Arctic; most consider it part of the Atlantic.

The Pacific Ocean is the world's largest at 64,000,000 square miles (166,000,000 square kilometers). The next in size is the Atlantic at 33,000,000 square miles (86,000,000 square kilometers). The smallest of the three is the Indian Ocean at 28,000,000 square miles (73,000,000 square kilometers). The Atlantic is divided into North Atlantic and South Atlantic regions, and the Pacific into North Pacific and South Pacific.

The...