Apparatus and methods are provided to minimize the escape of fuel out of a fuel tank when a tank wall is penetrated by a bullet. In one embodiment, a pressure differential may be maintained between a pressure within a fuel tank cavity and another pressure outside the fuel tank cavity in order to minimize the loss of fuel upon penetration of the fuel tank. In another embodiment, a compressed rubber layer of fuel-reactive rubber may be provided which is adapted to be attached to a fuel tank wall and to swell upon contact with fuel in order to substantially seal a penetrated hole in the fuel tank wall.