The invention relates to a method of optimizing the operating parameters (cathode pressure and operating temperature) in a low-temperature fuel cell. The parameters are selected in such a way that on the one hand, the maximum system efficiency which can be achieved in practice is essentially attained, and on the other hand, waste heat is produced by the fuel cell so that no external heat supply is required for operation. The method relates to operation with liquid fuel. The waste heat produced by the fuel cell amounts at a maximum to half of the electrical energy produced by the fuel cell.