In a proton exchange membrane fuel cell (FC), the gas diffusion layer (GDL) is identified as the component that is most affected by mechanical compression. In this article, a particular focus is provided on the methods to measure the three main electrical parameters—contact resistance, through‐plane resistance, and in‐plane resistance—of the GDL under compression. A nonlinear decrease of these resistances under compression is typically observed. In particular, an important decrease is observed from 0 to 2 MPa, then a lower one above 2 MPa. The smallest contact and in‐plane resistances are measured for the graphitized straight carbon papers analyzing GDL resistances under compression gives a first approach to explaining ohmic losses in FCs as a large part of these losses is related to the GDL. This review would be helpful for researchers in better understanding ohmic losses and establishing a database of main GDL electrical resistances and their variations according to several operating parameters. These data could be used in design models to optimize GDL properties.