Abstract This study presents a possible implementation of a second generation bioethanol production chain within the Province of Siena (Tuscany, Italy) by means of a biorefinery, and its consequences for the regional GHG balance in order to meet the European requirements for partial substitution of 10% bioethanol for gasoline by 2020. According to the last GHG balance of the territory of the Province of Siena, the transport sector represents the main contributor to the overall GHG emissions within the Province. A biorefinery project is hypothesized, fed by residual straw (from the local production of wheat, barley and oat) and residual geothermal heat (from local geothermal power plant) in order to produce bioethanol. The target of the production plant was about 8200 tons/year of bioethanol, representing the amount needed to replace 10% of the gasoline consumed in 2008 in the Province of Siena. The results of the Life Cycle Assessment (LCA) of the entire production chain have been included within the GHG balance of the Province of Siena in order to assess the effect of this substitution. The emissions derived from the production chain have been added to the current gross CO2eq emissions, and the CO2eq avoided, thanks to the substitution of bioethanol, has been subtracted. The main results of this paper are: 1) the territory of the Province of Siena produces enough straw to implement the bioethanol production chain (38,000 tons/year of ethanol out of 147,000 tons/year of straw); 2) the emissions deriving from the entire bioethanol production chain are about 601.51 kg CO2eq per ton of bioethanol produced (about 4932 tons of CO2eq are the emissions associated to the production of 8200 tons of bioethanol); 3) the use of the produced bioethanol in Siena's transport sector could bring about a reduction of 15,393 tons of CO2eq in emissions, equal to 6% of the net CO2eq emissions.