Abstract: A fuel tank for a motor vehicle, comprising a tank body with a smaller reservoir which is arranged therein and which is inserted into the tank body through a closable opening in the wall thereof, and joined thereto. The reservoir is deformable at least in portions of the wall defining same. After the reservoir has been at least partially inserted into the tank body, it undergoes a change in shape resulting in an increase in its volume within the tank body and a change in its cross-section such that the largest cross-section of the reservoir is larger than the cross-section of the opening of the wall in the tank body, that is available for insertion of the reservoir. The reservoir is defined at its ends by rigid components and the deformable wall portion of the reservoir is in the region between those components.