A packer apparatus 102 is disclosed and comprises a body 106 arranged to be disposed in a well casing. An activation member 104 is mounted to body 106 wherein the activation member is moveable relative to the body to deform an elastomeric packer element 108 outwardly relative to the body to form an annular seal in a well casing in use. A plurality of pistons 110 are arranged to move activation member 104 relative to the body. Each piston defines a respective pressure chamber 112 arranged to be filled with fluid in response to an increase in fluid pressure in the body 106 to move each of the plurality of pistons 110 relative to the body 106 and cause the activation member 104 to move relative to the body.