The present invention relates to a gas storage tank, for storing gas, especially CNG, methane and/or hydrogen, said tank comprising a liner comprising a high-viscosity polyamide composition comprising a branched polyamide and an impact modifier, and to a process for manufacturing said the tank. More particularly, the composition comprises a copolyamide of the random tree type resulting from the reaction between a multifunctional monomer comprising at least three reactive functions to form an amide function, these functions being of two different types, difunctional monomers conventionally used in the manufacture of linear polyamides, and optionally difunctional monomers.