In dry anaerobic digestion, biogas production is inhibited at high total solids contents. Such inhibition can likely be due to a slow diffusion of dissolved molecules into the digestate with subsequent local accumulation of inhibitory products. In this study, we investigated the impact of H2 and CO2 partial pressure on dry AD. Specific batch tests operated were carried out with thin layer to limit gas diffusion. Results showed that initial H2 partial pressure higher than 800 mbars had a strong inhibitory effect on methane production. The total substrate degradation yields were also impacted, indicating a direct inhibitory effect on hydrolysis. Interestingly, when H2 and CO2 were both added, they were consumed by homoacetogenesis/methanogenesis until CO2 was completely exhausted. CO2 was found to be the limiting element in case of H2 inhibition. The reversibility of H2 inhibition was also investigated by adding CO2 at different reaction times. Results showed that hydrolysis and methanogenesis inhibitions were fully reversible after CO2 addition even after 18 days of operation. Our results give new insights on probable effect of local gas accumulation in dry AD processes.