The first offshore drillship was the CUSS 1 developed for the Mohole project to drill into the Earth's crust. As of June 2010, there were over 620 mobile offshore drilling rigs (jackups, semisubs, drillships, barges, etc.) available for service in the worldwide offshore rig fleet. One of the world's deepest hubs is currently the Perdido in the Gulf of Mexico, floating in of water. It is operated by Royal Dutch Shell and was built at a cost of $3 billion. The deepest operational platform is the Petrobras America Cascade FPSO in the Walker Ridge 249 field in of water. Main offshore fields Notable offshore fields include: the North Sea the Gulf of Mexico (offshore Texas, Louisiana, Mississippi, and Alabama) California (in the Los Angeles Basin and Santa Barbara Channel, part of the Ventura Basin) the Caspian Sea (notably some major fields offshore Azerbaijan) the Campos and Santos Basins off the coasts of Brazil Newfoundland and Nova Scotia (Atlantic Canada) several fields off West Africa most notably west of Nigeria and Angola offshore fields in South East Asia and Sakhalin, Russia major offshore oil fields are located in the Persian Gulf such as Safaniya, Manifa and Marjan which belong to Saudi Arabia and are developed by Saudi Aramco. fields in India (Mumbai High, K G Basin-East Coast Of India, Tapti Field, Gujarat, India) the Taranaki Basin in New Zealand the Kara Sea north of Siberia the Arctic Ocean off the coasts of Alaska and Canada's Northwest Territories Challenges Offshore oil and gas production is more challenging than land-based installations due to the remote and harsher environment. Much of the innovation in the offshore petroleum sector concerns overcoming these challenges, including the need to provide very large production facilities. Production and drilling facilities may be very large and a large investment, such as the Troll A platform standing on a depth of . Another type of offshore platform may float with a mooring system to maintain it on location. While a floating system may be lower cost in deeper waters than a fixed platform, the dynamic nature of the platforms introduces many challenges for the drilling and production facilities. The ocean can add several thousand meters or more to the fluid column. The addition increases the equivalent circulating density and downhole pressures in drilling wells, as well as the energy needed to lift produced fluids for separation on the platform. The trend