Abstract: A bladder for a fuel tank includes plural concentric chambers separated by respective walls for placement in a fuel tank to contain fuel in such chambers, spacers for spacing the outer walls forming the respective chambers from the inner wall of a fuel tank, a bottom wall with openings to allow filling of the respective chambers from the bottom, a cover to block flow of fuel out from the top of the chambers, vents in the cover to permit air to exit the respective chambers, and a combination seal and dike at respective vents to block fuel flow into the vents from the top and to block fuel from exiting through the vents during impact that tends to collapse the fuel tank and bladder.