Purpose: This paper aims to investigate whether providing voluntary external assurance on voluntary environmental information by firms operating in environmentally sensitive industries (ESI) is relevant in terms of market value. It also examines how various characteristics of assurance statements (i.e. level of assurance, scope of assurance and provider of assurance) affect the value-relevance of environmental disclosure by ESI firms. Design/methodology/approach: To mitigate the endogeneity problem, the authors use the two-step generalized method of moments estimation approach. Findings: Focusing on annual and social reports of French companies listed in the SBF120 index, results show that environmental disclosure by ESI firms and its assurance are destructive in terms of market value. Moreover, while providing a broader scope of assurance and having a professional accountant as the assurance provider enhance the value relevance of environmental reporting of the whole sample, this is unlikely to be the case for ESI firms. In particular, a higher level of environmental disclosure is financially rewarded by market participants for ESI firms that provide a higher level of assurance. Practical implications: The study provides a better understanding of the circumstances under which market participants assign value to voluntary environmental information disclosed by companies operating in ESI. It also provides insights into the value added to different characteristics inherent in the quality of assurance provided with regard to environmental disclosure. Social implications: The study indicates that the institutional context of the relationship between the firm and its shareholders influence the value obtained from assurance. Results provide value insights regarding cultural and legal dimensions of environmental reporting. Originality/value: The study extends the prior literature on the capital market benefits of voluntary assurance practices by focusing on the French legal environment. France can be considered as a new institutional context that has been little addressed by the existing literature.