Abstract This paper discusses the laws of the fuel consumption in a polymer electrolyte fuel cell and its related performance. Based on simplifying but realistic approximations these laws are presented in analytical form. We verify these laws with space resolved current–voltage measurements in a single channel fuel cell. The results give a clear picture of the inside-the-cell distribution of performance associated with reactant consumption. This picture helps to rationalize the modes of optimal fuelling and is lessening for design of the flow-fields.