Research on the outcomes of Corporate Social Responsibility (CSR) on firm performance have garnered much interest in recent years, reflecting investors growing awareness of social, environmental and corporate governance issues. The literature in this field, though vast, is littered with contradictory evidence. In addition, most studies lack a coherent set of metrics to assess CSR. Using a differentiated approach, in which firms social responsibilities are evaluated within a multidimensional framework considering information from their annual social reports, this work aims to examine the relationship between CSR and firm performance in the Brazilian electric sector in recent years. The analysis is conducted in two basic steps: first, the Brazilian electric companies are classified according to the information disclosed from their social reports using a Data Envelopment Analysis Model. Then, several portfolios are formed based on firms Environmental, Social and Governance (ESG) performances and are subsequently assessed using different financial metrics. The sample comprises a total of 36 electric companies and the time period of the analysis spans from 2009 to 2013. The results from both ex-post and ex-ante evaluations clearly indicate that portfolios comprising assets from firms with the best ESG practices not only offered the highest excess returns per unit of risk but also presented the lowest probabilities of large losses during the analysis period. In addition, firms that presented lower ESG performances but also released social reports during the years of portfolio formation performed significantly better than firms that did not disclose any social information within this time span.