The Gulf of Mexico is an ocean basin largely surrounded by the North American continent. It is bounded on the northeast, north, and northwest by the Gulf Coast of the United States, on the southwest and south by Mexico, and on the southeast by Cuba. The U.S. states of Texas, Louisiana, Mississippi, Alabama, and Florida border the Gulf on the north, which are often referred to as the "Third Coast" in comparison with the U.S. Atlantic and Pacific coasts, or sometimes the "south coast", in juxtaposition to the great lakes region being the "north coast".
The Gulf of Mexico formed approximately 300 million years ago as a result of plate tectonics. The Gulf's basin is roughly oval and is approximately 810 nmi wide and floored by sedimentary rocks and recent sediments. It is connected to part of the Atlantic Ocean through the Florida Straits between the U.S. and Cuba, and with the Caribbean Sea (with which it forms the American Mediterranean Sea) via the Yucatan Channel between Mexico and Cuba. With the narrow connection to the Atlantic, the Gulf experiences very small tidal ranges. The size of the Gulf basin is approximately 615,000 mi² (1.6 million km²). Almost half of the basin is shallow continental shelf waters. The basin contains a volume of roughly 660 quadrillion gallons (2.5 × 106 km3).