This article develops a least-cost optimization model in terms of the projected SO2 abatement costs of nine selected options for SO2 emissions control in the 10 most polluting power plants of the Mexican electrical sector (MES)-including SO2 scrubbing technologies, fuel oil hydrotreating desulphurization and fuel substitutions. The model not only finds the optimal combination Of SO2 control options and generating units at 10% reduction intervals referred to the total SO2 emissions but also meets the restriction imposed in the NOW 085-ECOL-1994 (Mexican Official Norm) for allowable emission levels within critical zones. Similarly, two schemes are studied and analysed in this model: the first case considers the economical benefits derived from the substitution of fuel oil by imported low sulphur content coal in the Petacalco power plant and; the second case does not considered such economical benefits. Finally, results are obtained for these two cases in terms of the corresponding costs-investment, O&M, fuel-, abatement costs and the SO2 emissions reduction. (C) 2007 Elsevier Ltd. All rights reserved.