In this study, the effects of varying operating conditions on cell performance in cylindrical and planar PEM (Proton Exchange Membrane) fuel cells with equal geometrical properties are investigated numerically. For this purpose, planar and cylindrical fuel cells are analyzed and the changes in performance are compared with each other. In particular, by increasing the temperature from 363 to 373 K, the current density decreases by ≈50%. When the pressure is increased from 1 atm to 1.2 atm, the current density increases by 20% and 2% in cylindrical and planar fuel cells, respectively. When the stoichiometric ratio is increased from 1 to 1.5, the current density increases by 25% and 32% for cylindrical and planar fuel cells, respectively. However, it decreases slightly after 1.5 value of the stoichiometric ratio. As a result, it is seen that temperature has a more significant effect on fuel cell performance than other operating conditions. It can be said that the planar fuel cell can operate with more stable performance than the cylindrical fuel cell when the temperature and pressure are changed. However, in the case of changing the stoichiometric ratio, there is no significant difference in the operating performance of both fuel cells.