This study aims to analyze the level of environmental disclosure (ED) and its determinants. Employing a mixed-methods approach, this investigation employs content analysis in corporate reports spanning from 2016 to 2020. Furthermore, multiple regression analysis on panel data is utilized to identify the drivers of ED extent. Findings from this study indicate an upward trend in the ED index, which is slightly higher in Brazil, with the sustainability report, the most widely used means of disclosure, showing the highest levels of ED. Global Reporting Initiative (GRI) indicators related to environmental compliance, emissions, and energy exhibit the highest levels of disclosure. Moreover, GRI standards adoption, CEO duality, and workers diversity are identified as significant influencers of ED extent in both countries. This research contributes valuable insights to both academic literature and practical application by scrutinizing the extent of ED in private and listed Portuguese companies and identifying influential factors.