The present invention discloses an apparatus and method for rapid analysis of members of a combinatorial library. The apparatus includes a plurality of reactor vessels for containing individual library members, a fluid handling system that apportions a test fluid about equally between each of the vessels and a housing for enclosing the reactor vessels, the housing defining a pressure chamber, wherein the housing is configured to sustain a pressure substantially above atmospheric pressure. This allows for simultaneous screening of library members at high pressure by providing a small pressure differential on reactor components. The disclosed apparatus is especially useful for screening library members based on their ability to catalyze the conversion of fluid reactants.