In Buenos Aires metropolitan area, electrical energy distribution must comply with maximum supply interruption rates, imposed on distributors by Franchise Agreements. The calculation procedure of the corresponding discounts (bonus) includes the record of network contingencies, type of customer-network connection and non-supplied energy estimation. The control method which is described, comprises the record of interruptions at supply points and the following calculation of the corresponding bonus. By selecting these points with statistical sampling criteria, it is possible to determine the quality of the Utility global task performed by traditional methods. This method is similar to that one used to control electrical energy meters in service. The present starting-up stage of the method provides deterministic information about long term interruptions obtained from records of supply interruptions, carried out for about three years of systematic recording. Also recorded short interruptions (durations comprised between 10 sec. and 3 minutes) are analyzed. At present, these short interruptions are not penalized by the Argentine regulation, but this topic has increasing importance to qualify supply reliability to industries.Instituto de Investigaciones Tecnológicas para Redes y Equipos Eléctricos (IITREE)