There are many different types of facilities from which offshore drilling operations take place. These include bottom founded drilling rigs (jackup barges and swamp barges), combined drilling and production facilities, either bottom founded or floating platforms, and deepwater mobile offshore drilling units (MODU), including semi-submersibles and drillships. These are capable of operating in water depths up to . In shallower waters, the mobile units are anchored to the seabed. However, in deeper water (more than ), the semisubmersibles or drillships are maintained at the required drilling location using dynamic positioning.