A fuel tank for a vehicle includes a main tank comprising a first tank volume defined by an outside wall and an auxiliary tank extending from an aperture provided in the outside wall. The auxiliary tank is formed as a pocket-shaped continuation of the outside wall into the first tank volume bounded by the outside wall. The auxiliary tank forms a second tank volume which is separated from the first tank volume and opens into a filler neck which runs inside the first tank volume and emerges on the outside wall of the main tank.