The objective of this research is to develop a comprehensive and effective quantitative method to measure the overall sustainability performance of electric companies in Italy. Due to the vast diversity of the sustainability issues, many methods have been developed to measure the sustainability performance of companies, but with results that are, in our opinion, not fully satisfactory, either because they are difficult to apply or because they only cover some of the sustainability aspects. In an attempt to overcome these shortcomings, we have applied a methodology to meet the requirements of our research, on the basis of its high versatility (https://lab24.ilsole24ore.com/qualita-della-vita/). The analysis was carried out on the 12 largest Italian electricity companies, by calculating the overall sustainability index (OSI) for the years 2020 and 2021, taking into account 56 different indicators, chosen from those made available by the Global Reporting Initiative (GRI) for corporate sustainability reporting. For a more comprehensive evaluation of the sustainability performance of the electricity companies, selected indicators were chosen from all the three pillars of sustainability (economic, environmental, social). The OSI results of this research have allowed to highlight the critical points of the corporate reporting systems on sustainability providing valuable indications on the targets achieved and achievable in view of the European Commission's Green Deal 2050. This work also highlighted the strengths and weaknesses of the method.