Closure system on a fuel tank

Closure system on a fuel tank comprising an opening in the wall of the fuel tank and a closure cover which covers the opening and clamps at least one elastomer seal between itself and a border of the tank wall enclosing the opening, wherein the elastomer seal is formed as a multilobed sealing cord or multilobed sealing ring surrounding the opening, in such a way that it forms a number of sealing lips that are spaced apart from one another, at least two spaced-apart sealing lips of the elastomer seal consisting of different materials, one of which is substantially impermeable to hydrocarbons and a second is substantially impermeable to alcohol-containing media or alcohol-containing additives wherein the the elastomer seal has an approximately H-shaped cross-sectional profile with a first limb and a second limb and with a crosspiece connecting the limbs, the limbs respectively consisting of different elastomeric materials, characterized in that the crosspiece connecting the limbs consisting of a thermoplastic material.