BOP. (1) A safety device for closing the [[wellhead]], which has rubber [[rams]] which can be closed down on the logging [[cable]] in the event the well begins to blow out. Blowout preventers may be connected in series for improved control. See illustration at [[lubricator]]. See also [[riser]], [[stuffing box]], [[hydraulic packing head]], and [[flow tube]].

(2) Equipment installed at the wellhead at surface level on land rigs and on the seafloor of floating offshore rigs to prevent the escape of pressurized fluids either in the [[annular space]] between the [[casing]] and [[drill pipe]] or in an open hole during drilling and completion operations. See also [[rams]].