An air bag apparatus is installed along the front-to-rear axis of the interior-facing side roof rail of a vehicle. The air bag has an air bag body, an inflator and a fluid body supply device. The air bag body has a plurality of inflatable chambers with at least one specific chamber and at least one general chamber. When in the deployed state, the specific chamber is positioned adjacent a structural pillar member of a vehicle side portion of the vehicle body. When in the deployed state the general chamber is located adjacent the vehicle side portion. In use, the inflator supplies a high-pressure fluid to the air bag body thereby inflating each of the chambers and the fluid supply delay device selectively delays the high-pressure fluid to the specific chamber relative to the general chamber.