Gulf of Mexico numerous bays and smaller inlets. A number of rivers empty into the gulf, most notably the Mississippi River and Rio Grande in the northern gulf, and the Grijalva and Usumacinta rivers in the southern gulf. The land that forms the gulf's coast, including many long, narrow barrier islands, is almost uniformly low-lying and is characterized by marshes and swamps as well as stretches of sandy beach. The Gulf of Mexico is an excellent example of a passive margin. The continental shelf is quite wide at most points along the coast, most notably at the Florida and Yucatán Peninsulas. The shelf
Offshore oil and gas in the Gulf of Mexico (United States) Gulf Coast Florida, has never been a petroleum-producing area. From the 1950s to the 1990s, oil companies drilled exploratory wells off the Gulf Coast of Florida. Nineteen wells were drilled in state waters, and forty were drilled in federal waters. Gulf Oil drilled the first offshore Florida oil exploration wells in 1947, in state waters in Florida Bay south of Cape Sable, Monroe County. In 1956 Humble Oil drilled an exploratory well in state waters of Pensacola Bay, Santa Rosa County. In 1959 Gulf Oil drilled the first offshore Florida well drilled from an offshore platform, off the Florida Keys.