A perforating tool usable in a well casing to perforate the well casing. Perforating tool includes an activation member disposed in body wherein the activation member is moveable relative to the body to move at least one working member between and inwardly retracted condition an outwardly deployed condition relative to the body. A plurality of pistons is arranged to move the activation member relative to the body, each piston being disposed in a respective pressure chamber arranged to be filled with fluid in response to an increase in fluid pressure in the body.