Mexico, Gulf of, an arm of the Atlantic Ocean off the southeastern coast of North America. It is crossed by the Tropic of Cancer and is almost encircled by the United States, Mexico, and Cuba. The Yucatan Channel links the gulf with the Caribbean Sea; the Straits of Florida lead to the Atlantic Ocean.

The gulf covers some 582,000 square miles (1,500,000 km2) and has a maximum depth of 14,358 feet (4,376 m) in the Mexican Basin. A broad continental shelf, up to 200 miles (320 km) wide, lies at depths of less than 600 feet (180 m) along the edge of the gulf, especially in the vicinity of the United States and the Yucatan peninsula of Mexico. Except for the Bay of Campeche, in the south, the gulf has no large extensions.

Relatively small bays and lagoons, however, are numerous along the coast.

The gulf receives water from torrential rains and from many rivers, most notably the Mississippi. In addition, part of the Atlantic's North Equatorial Current enters the gulf through the Yucatán Channel. Issuing from the gulf by way of the Straits of Florida is the Gulf Stream, an enormous current of warm tropical water that veers northeastward across the Atlantic.

Economically, the gulf is probably most important as a source of petroleum, especially in Texas and Louisiana, where offshore wells tap large reserves in the continental shelf. The gulf also yields an abundance of seafood and provides sea routes, including part of the Intracoastal Waterway of the United States. Resorts, recreation areas, and wildlife refuges line some portions of its shore. Principal ports on or near the gulf include New Orleans, Houston, Mobile, and Tampa in the United States; Veracruz and Tampico in Mexico; and Havana in Cuba.

Explorations in the gulf were first made by Spaniards early in the 1500's. In 1513, after discovering Florida, Juan Ponce de Leon sailed the south Florida coast. Five years later, in 1518, most of the Mexican coast, from Yucatán westward, was explored by Juan de Grijalva. The northern coast, from Florida to Mexico, was charted by Alonso Alvarez de Pineda in 1519.