It was suggested in the literature that the low Tafel slopes observed on Raney Ni electrodes may be due to hydrogen pressure build-up in pores. In the present paper, equations describing hydrogen distribution in pores were developed and the effect of hydrogen build-up on the observed currents was examined. These studies indicate that assuming very narrow pores and extremely active electrodes, a low Tafel slope of similar to 47 mV dec(-1) may be obtained. However, such an effect could be observed on very active electrode materials and only at very low overpotentials, before the bubbles are formed and, in practice, it is negligible. Equations developed were also applied to the electrode structure optimization for the hydrogen oxidation reaction.