Abstract:This study has two main purposes. First, it explores the performance indicators disclosed in the Global Reporting Initiative (GRI)-based Sustainability Reports (SRs) produced by the companies of three different countries: Italy, Spain and Greece. Second, it verifies how some corporate variables, country of origin variables and "attributes" of the SRs can explain the disclosure of GRI indicators. To verify the quantity and type of the indicators disclosed, we performed a content analysis of the SRs. We use a regression trees technique to describe how the companies' variables explain a different use of the indicators. The findings show that Spanish companies, on average, disclose the greatest number of indicators. The social indicators related to Labour are those more frequently reported in the SRs of the three countries. The least reported are social indicators related to Human Rights. The results show the central role that assurance, ROA and sector may have in classifying the disclosure level of indicators. The study contributes both theoretical and empirical literature on sustainability indicators. It also sheds further light on the determinants of the disclosure of indicators.