Abstract This paper presents an application of a methodology for the diagnosis and analysis of the service quality perceived by a Particular Group of CELPE Corporate Customers, a Brazilian power company at Pernambuco State. Concepts, on the power sector, of Quality in Services, Performance Objectives and Critical Factors of Success have been used to develop the analysis. Next, the Critical Factors for a power company were determined and classified in accordance with the performance objectives: Quality, Dependability, Speed and Flexibility. From the factors established, a questionnaire was created to collect data. The case studied involves quantitative research on CELPE's private corporate principal customers using statistical tests to measure internal consistency reliability of the questionnaire scales and to identify underlying concepts, in the four groups analyzed, through which the private corporate customers perceive quality in the given services. Among the goals of this study are to improve the relationship with principal Private Corporate Clients, to create customer loyalty, and to maximize efforts in providing the power supply service, all of them with a view to improving and determining the Global Satisfaction Index.