Nations or regions with limited electrical grid and restricted financial resources are a suitable market for small medium power plants with a size of 300-400 MWe. The literature present's several comparisons about the economics of large power plants (of about 1000 MWe); however there are not probabilistic analysis regarding the economics of small medium power plants. This paper fills this gap comparing, with a Monte Carlo evaluation, the economical and financial performances of a nuclear reactor, a coal fired power plant and a combined cycle gas turbine (CCGT) of 335 MWe. The paper aims also to investigate the effect of the carbon tax and electrical energy price on the economics of these plants. The analysis show as, without any carbon tax, the coal plant has the lowest levelised unit electricity cost (LUEC) and the highest net present value (NPV). Introducing the carbon tax the rank changes: depending on its amount the first and the nuclear after becomes the plant with lower LUEC and highest NPV. Therefore, the uncertainty in the carbon tax cost increases the risk of investing in a coal plant above the level of the new small medium reactor. (C) 2010 Elsevier Ltd. All rights reserved.