fig1 diagrammatically depicts a fuel tank in longitudinal section , having a chamber 2 for holding fuel and having two shell parts 3 , 4 . a compensation tank 5 arranged in the fuel tank 1 has a housing part 6 of pot - shaped configuration and is secured to the upper of the shell parts 4 by material - to - material bonding . the upper shell part 4 has an edge 7 for this purpose . the base region of the pot - shaped housing part 6 of the compensation tank 5 is produced integrally with a housing part 8 of an activated carbon filter 9 . the housing part 8 is joined to a cover 10 by material - to - material bonding . the activated carbon filter 9 has a cartridge 11 comprising activated carbon which has been inserted into the housing part 8 . of course , the activated carbon filter 9 can also be produced by activated carbon being introduced into the housing part 8 . vent lines 12 lead into the compensation tank 5 through the upper edge 7 of the shell part 4 of the fuel tank 1 . the activated carbon filter 9 is likewise connected to the inner region of the compensation tank 5 via a vent line 13 . a further vent line 14 leads through a common region of the wall of the fuel tank 1 with the compensation vessel 5 into the environment . as a result , for example in the event of thermal expansion of the fuel in the chamber 2 , gases can flow through the vent lines 12 into the compensation tank 5 and , from there , through the activated carbon filter 9 into the environment . furthermore , a base valve 15 which ensures that liquid fuel which has penetrated into the compensation tank 5 is returned to the chamber 2 is arranged in the base region of the compensation tank 5 . on account of the position at which it is arranged , the activated carbon filter 9 in the compensation tank 5 is substantially protected from contact with liquid fuel . fig2 shows a compensation tank 16 for the fuel tank 1 from fig1 . this differs from that shown in fig1 substantially through the fact that a cover 17 of an activated carbon filter 18 arranged inside the compensation tank 16 has connections 19 and is connected to plug connections 20 arranged in the upper region of the wall . moreover the activated carbon filter 18 has a double - walled housing 21 . fig3 shows a compensation tank 22 which is intended to be secured in a fuel tank ( not shown ). the compensation tank 22 has two housing parts 23 , 24 which are welded to one another and , in the base region , a molded formation 25 for holding an activated carbon filter 26 . a partition 27 for separating off the activated carbon filter 26 is welded to the base region of the compensation tank 22 . a connection 28 for a vent line leads through the partition 27 . this activated carbon filter 26 too has a cartridge 29 inserted into the molded formation 25 of the compensation tank 22 . fig4 shows a compensation tank 30 which is of particularly simple design and in which an activated carbon filter 31 is secured to the lower of two housing parts 32 , 33 of the compensation tank 30 . vent lines ( not shown ) can be connected to the compensation tank 30 and the activated carbon filter 31 .