In order to accommodate expansion and contraction in a fuel system, even in the presence of extremes of temperature, while maintaining the fuel system pressure at ambient, a thermal expansion reservoir is provided. The thermal expansion reservoir includes a rigid housing having releasably interconnected first and second housing portions provided with a fluid inlet port and a vent. A resilient bladder is disposed within the housing between the inlet port and the vent in a manner dividing the housing into a fluid expansion chamber and a pressure relief chamber, each of variable size depending upon the fluid pressure in the fluid expansion chamber. A redundant seal arrangement is integrally associated with the resilient bladder to form primary and secondary seals between the housing portions while joining the resilient bladder to the housing. The thermal expansion reservoir is also formed such that the resilient bladder has a first wall portion leading from the housing in the direction of the vent to a return bend and a second wall portion leading from the return bend in the direction of the inlet port to an end cap. With this construction, the return bend initiates rolling of the second wall portion toward the vent and the second wall portion is tapered to promote rolling of the second wall portion toward the vent in an automatically controlled and substantially frictionless fashion.