This work analyses future energy scenarios at country scale, focusing on the interaction between power and transport sectors, where Power-to-Gas is expected to play a key role. A multi-node model is developed to represent the integrated energy system, including additional electrical load from plug-in electric vehicles, energy storage, and hydrogen production from excess electricity for fuel cell vehicles. Electricity supply-demand balance is solved hourly, while liquid and gaseous fuels for mobility are accounted for cumulatively over the year. The Italian system is investigated, considering different evolution scenarios up to 2030 and 2050. The simulations yield a maximum 57% share of renewable sources in the electricity mix in 2050, while biomass could account for a further 5%. Results show that the use of Power-to-Gas increases the overall share of renewable sources across the sectors. High coverage of hydrogen mobility demand by clean production (about 81%) is achieved in presence of a large installation of renewables and a substantial introduction of fuel cell vehicles. However, greenhouse gas emissions reduction does not attain the ambitious long-term targets. In the best scenario, transport approaches the 60% cut, while power sector achieves only half of the desired 95% variation, thus calling for additional measures. (C) 2018 Elsevier Ltd. All rights reserved.