All four bodies of water are different in size and location. Oceans, rich in seawater, are the largest bodies of water. There are four oceans: the Pacific, the Atlantic, the Indian, and the Arctic. At the edges of the oceans are seas, a part of the ocean that is partially enclosed by land. For example, the North Sea borders the Atlantic Ocean. (Not every body of water with the word “sea” in it is a sea: the Caspian Sea, Dead Sea, and Aral Sea are actually saltwater lakes because they lack an outlet to the ocean.) Gulfs and bays are bodies of water that jut into the land; a gulf is larger, sometimes has a narrow mouth, and is almost completely surrounded by land. The world’s largest gulf is the Gulf of Mexico, with a total surface area of about 600,000 square miles (1.5 million square kilometers). It is surrounded by Mexico, the southern coast of the United States, and Cuba, and contains many bays, such as Matagorda Bay in Texas and Mobile Bay in Alabama. The San Francisco Bay, off the coast of northern California, is a well-known bay in the United States.