Regulatory pressure and the Diffusion of Sustainability Reporting Assurance: Evidence from the European and United States context

This thesis presents a comparative empirical analysis of Sustainability Reporting Assurance (SRA) among large listed firms in the European Union and the United States. The study is based on a manually constructed dataset covering assurance adoption, assurance level, provider type, applied standards, and greenhouse gas disclosure practices. The results reveal a clear structural divergence between the two jurisdictions. European firms display significantly higher assurance adoption rates and more standardized verification practices, reflecting the institutionalization of sustainability reporting and the transition toward mandatory assurance. By contrast, U.S. firms operate within a predominantly voluntary regime, where assurance is not supported by a binding regulatory framework and consequently appears more discretionary and heterogeneous in scope. The findings indicate that sustainability assurance is strongly shaped by institutional context. In environments characterized by coercive regulatory pressure, assurance tends to be more prevalent and procedurally consistent. In voluntary settings, assurance remains uneven and more closely linked to reputational incentives. Overall, the thesis provides evidence that the presence or absence of a mandatory regulatory framework plays a central role in shaping the diffusion and configuration of sustainability reporting assurance across advanced economies.