In one embodiment, a parallel batch reactor for effecting chemical reactions includes a plurality of reactor vessels for receiving components of a reaction, an inlet port for receiving pressurized fluid, and a plurality of valves configured to transfer fluid from the inlet port to the reactor vessels and fluidically isolate one or more of the reactor vessels from at least one of the other reactor vessels. The reactor further includes a pressure monitoring system comprising an array of pressure sensors configured to sense pressure in the reactor vessels. Each of the pressure sensors is aligned with one of the plurality of reactor vessels and located external to the reactor vessels and fluid passageways in fluid communication with the reactor vessels.