A fuel cell system including at least two reformer units for catalytic decomposing a starting material stream into at least one intermediate product and one hydrogen-rich fuel stream of a fuel cell unit, in which each reformer unit converts the starting material stream into an end product stream in at least one first operating phase and into the intermediate product in a second operating phase using an auxiliary material stream. The fuel cell system provides its continuous generation of a hydrogen-rich fuel stream from hydrocarbons for mobile and/or stationary fuel cell applications using at least one heat exchanger unit to exchange heat between the reformer units.