Abstract: A downhole relief valve connected to a tubing string in a producing well above the packer for controlling the well to prevent excess pressure built up in the annulus and casing damage following a tubing rupture at a point where the flowbore pressure exceeds the annulus pressure. The valve has a housing, fluid communication means between the flowbore and the annulus and a piston mounted within the housing for reciprocating between an open position and a closed position to allow flow in the fluid communication means between the flowbore and the annulus. The piston is biased to the closed position by compressed gas and/or a shear pin and to the open position by the hydraulic force exerted by the fluids from the casing annulus. If the hydraulic force exerted by the fluids from the casing annulus exceeds the forces biasing the piston to the closed position, the piston moves to the open position and fluid from the casing annulus flows into the flow bore and kills the well.