The paper aims to analyse the impact of "pigouvian taxation" on energy products in Italy and in Europe. It consists of two sections. In the first the impact (on the interfuel competition) of replacing present excise taxes with external costs is simulated in Italy and in Europe. In the second section, after simulating the effects related to the adoption of a common environmental taxation (a first best solution based on the internalisation of environmental external costs), a second best solution is proposed (an excise taxes harmonisation model). This model proposes: the introduction of a minimum level of taxation on all products equal to the external cost due to the greenhouse effect (a common carbon tax); the possibility, given to the Member States, of deviating from such minimum levels, in accordance with their specific requirements, internalising in the price of the different products (by means of taxes additional to that CO2 minimum) the external costs associated with other pollutant agents (the same in all countries).