Abstract: A blowout preventer having a mechanical linkage to a valve connected to a pressure relief line in the casing beneath the blowout preventer whereby the valve on the pressure relief line is opened when the blowout preventer is actuated is disclosed. The blowout preventer includes an upright tubular body having an annular packing therein which can be constructed about a drill pipe or other pipe in the well, a head connected to the top of the upright tubular body for containing the annular packing in the body, a piston slidably received in the body and adapted to selectively constrict the packing about the well pipe, a casing pipe connected to the lower end of the body for containing the well pipe, a pressure relief line connected to the casing having a valve therein, and a rod connected to the piston and the valve to open the valve when the piston slides within the tubular body to constrict the packing about the well pipe.