The objective of the presented work is to study the operating parameters and their effects on the performance of an air breathing PEM fuel cell. In this study, we have theoretically calculated the losses associated with the fuel cells. The performance of the fuel cell can be determined by using the polarisation curve. Polarization curves from which the output voltage can be found are studied in detail. The drop in cell voltage occurs due to several irreversibility in the working environment. Reduction in resistance due to activation energy, mass transport and charge transport can help in increasing the performance of the Fuel cells. The performance of a fuel cell is also affected by the factors such as exchange current density, transfer coefficient. The operating parameters like pressure, temperature are varied and the performance of the PEM fuels cells is recorded.