An apparatus and a method are used for investigating the naphtha reforming process in catalyst test devices with reactors arranged in parallel. The apparatus has a plurality of reactors arranged in parallel with reaction chambers (R1, R2, . . . ), a product fluid supply, a process control, and at least one analysis unit. Each individual reactor has an outlet line for the product fluid stream, wherein the analysis unit is operatively connected to each outlet line for the product fluid stream and the apparatus is functionally connected to the control of the apparatus. In carrying out the method, naphtha-containing reactant fluid streams are brought into contact with catalysts in the individual reactors and the product fluid streams are subsequently supplied to the online analysis unit from the respective outlet lines of the individual reactors and analyzed. Using the evaluation of the online analytical characterization data, the process parameters of the respective reactor unit are adapted. The process steps of analytical characterization, evaluation, and adaptation of process parameters are repeated for the duration of the investigation.