These are mechanical devices provided by the drilling contractor and used during the drilling of a well to provide protection from an unexpected flow of oil or gas from a well. Blowout preventers (BOPs) provide a means to shut the well in should a dangerous flow of oil or gas occur. The BOPs sit directly under the drill floor and are connected to the casing. When a well starts to flow unexpectedly, the BOPs can be closed over the drill pipe or over an open hole to contain the flow. BOP equipment is much more complex for offshore operations and can be placed on the ocean floor or at the surface. These devices are very expensive and are kept in top condition. Hydril and Cameron Iron Works are the major manufacturers of the BOPs.