When it comes to drilling for oil, not all the resources are accessible from dry land. In order to extract oil from those hard-to-reach underwater oil fields, oil companies look to offshore drilling techniques to get the oil flowing. The process of offshore drilling involves fixed platforms on the water's surface, jack-up drilling rigs, floating drilling rigs or floating production storage and offloading units. Types of offshore operations Drilling operations vary depending on the type of platform and rig used to access oil offshore, the type of oil being recovered and the water depth. Energy companies are exploring for oil in oceans around the world, drilling in water depths from 300 feet to more than 10,000 feet. Surface wells drilled offshore are similar to those drilled on land. For these wells, the platform acts as an artificial island, the casing is brought back up from the well and a land-style wellhead and production equipment is used. Subsea wells, however, can be found at the ocean floor and require more specific drilling and production equipment. Fixed rigs are built in place on the ocean floor and have a number of well heads. Offshore oil drilling began in the Gulf of Mexico While oil companies first began drilling wells in the ocean in the late 1800s, it wasn't until March 1938 that the first freestanding structure was built in the ocean and the first well was drilled, according a report issued by the National Commission on the BP Deepwater Horizon Oil Spill and Offshore Drilling. This well was located in the Gulf of Mexico 1.5 miles off the coast of Louisiana in the Creole Field. The first productive well drilled "out-of-sight-of-land" in 1947 by Kerr-McGee Oil Industries. It was located 10.5 miles off the Louisiana coast in the Ship Shoal area, according to the report.