A locking gas spring incorporates a mechanism to enable the rod to be locked at any point in its travel. This mechanism is actuated by a plunger that protrudes from the rod. When this plunger is depressed the rod is free to operate as normal. When the plunger is released, which may be at any point in the stroke, the rod is locked in that position. This locking mechanism operates when the plunger rod is depressed by opening a valve in the piston. When the plunger rod is released the valve closes and the passage of oil or gas is prevented, locking the piston in that position.