There has been total unanimity about the vital importance of reliability of supply since the beginning of the electricity sector deregulation process. This paper describes the procedure proposed by Perez-Arriaga et al. [2005. White paper for the reform of the regulatory scheme of the power generation in Spain. For the Ministry of Industry, Tourism and Trade of Spain (in Spanish)] to improve upon the current scheme to guarantee a reasonable reserve margin, the capacity payment mechanism. This alternative design introduces improvements aimed at guaranteeing at least a minimum capacity reserve margin, as well as at providing a strong incentive for generating units to be available when needed, namely, in situations when supply is likely to be insufficient to meet the total demand. (C) 2007 Elsevier Ltd. All rights reserved.