The parallel screening apparatus is a semi-conventional UHV-chamber equipped with AES, SEM, SAM, XPS, ISS, TPD and a high pressure cell. Furthermore, it has the capability of deposition up to four different metals at the same time in spot diameters of 1 or 2 mm. Up to 10 spots of different compositions can be deposited on a substrate - e.g. a metal single crystal or a graphite sample. Subsequently, and after characterization, the sample can be brought out in the high pressure cell where the reactivity of each individual spot can be determined under pressures up to one bar and max 700ºC. In this manner it is possible to screen for good catalysts.