Parallel flow reaction systems comprising four or more reaction channels are disclosed. Distribution systems, and parallel flow reaction systems comprising such distribution systems are also disclosed. Specifically, the distribution systems comprise one or more subsystems, including for example, a flow-partitioning subsystem for providing a different flow rate to each of the four or more reactors, a pressure-partitioning subsystem for providing a different reaction pressure in the reaction cavity of each of the four or more reactors, and a feed-composition subsystem for providing a different feed composition to each of the four or more reactors. In preferred embodiments, the one or more subsystems can comprise at least one set of four or more flow restrictors, each of the four or more flow restrictors having a flow resistance that varies relative to other flow restrictors in the set.