This paper quantifies the contribution of Portuguese energy policies for total and marginal abatement costs (MAC) for CO2 emissions for 2020. The TIMES_PT optimisation model was used to derive MAC curves from a set of policy scenarios including one or more of the following policies: ban on nuclear power; ban on new coal power plants without carbon sequestration an storage: incentives to natural gas power plants: and a cap on biomass use. The different MAC shows the policies' effects in the potential for CO2 abatement. In 2020, in the most encompassing policy scenario, with all current and planned policies, is possible to abate only Lip to +35% of 1990 emissions at a cost below 23 epsilon t/CO2. In the more flexible policy scenarios, it is possible to abate up to - 10% of 1990 emissions below the same cost. The total energy system costs are 10-13% higher if all policies are implemented-76 to 101 B epsilon-roughly the equivalent to 2.01-2.65% of the 2005 CDR Thus, from a CO2 emission mitigation perspective, the existing policies introduce significant inefficiencies, possibly related to other policy goals. The ban on nuclear power is the instrument that has the most significant effect in MAC. (C) 2008 Elsevier Ltd. All rights reserved.