An inflatable curtain airbag can be used to cushion an occupant during a vehicle collision as well as retaining the occupant within the vehicle during a rollover event. Curtain airbags that do not extend to the vehicle's waist line may allow the occupant to fit between the bottom of the curtain airbag and the waistline, and thereby be ejected from the vehicle. This risk is increased with vehicles that do not have vertical pillars between the doors and windows of the vehicle. Increasing an inflation gas volume capacity of a lower portion of the airbag, may mitigate the risk of occupant ejection, if the increased volume portion of the curtain overlaps the vehicle pillars. The lower portion of the curtain airbag may have a first chamber and a separate second chamber.