Abstract: A hydrogen fuel cell stack has at least two segments of fuel cells each having reactant gas passages. The reactant gas passages of each fuel cell in each segment are arranged in parallel with each other. Flow of fuel cell fluids is in a gravity assisted downward direction. Gravity assisted flow directs water formed in each cell to lower removal points of the stack segments. Adjacent segments are separated by either a separator segment formed as an integral unit with the stack or the segments are joined and an external piping system directs flow to differing stack areas. A cathode flow enters at a first stack end and a hydrogen anode flow enters the stack at an opposite end, such that cathode and anode flows are counter-current to each other. A coolant flow is normally injected adjacent to and flows parallel with the cathode flow, but can also be directed by the piping system to any or all segments in series or parallel.