Abstract: An engine assembly 10 includes an inner housing 12 containing an engine in an outer housing 14 disposed about the inner housing 12 and defining a sealed chamber 16 therebetween. A fuel storage bladder 20 disposed within the chamber 16 in fluid communication with the engine through the inner housing 12. The bladder 20 includes a first wall 24 and a second wall 26 and a peripheral seam for perfecting a peripheral fuel-tight seam interconnecting the first and second walls 24, 26. The walls 24, 26 are flexible for bowing away from each other to contain fuel therebetween and lie against each other upon the application of fluid pressure from a pressure source 18. Each of the walls 24, 26 have an inner surface 28, 30 facing the inner surface of the other of the walls, the inner surfaces 28, 30 having an equal surface area whereby the inner surfaces 28, 30 completely engage each other when the bladder 20 is emptied of fuel.