Firms are increasingly turning to voluntary carbon markets to offset emissions as part of their net-zero strategies. However, the factors shaping corporate motivations, behavioural drivers, and preferences for carbon offsets have received limited academicattention. Drawing on the Theory of Planned Behaviour and integrating it with a Discrete Choice Experiment, this study examines the behavioural and preferences-based factors influencing Spanish firms’ decisions to offset greenhouse gas emissionsthrough forest-based carbon removal projects. The analysis compares firms participating in the Carbon Footprint Registry, a government-led voluntary mechanism for climate disclosure and mitigation efforts, with firms operating outside formal disclosure frameworks. The results indicate that, for Registry firms, subjective norms, particularly stakeholder expectations and competitor behaviour, together with positive internal attitudes, constitute the main drivers of offsetting behaviour. In contrast,non-registered firms’ decisions are driven primarily by perceived control, economic considerations, and peer influence, with attitudes playing a more limited role. The findings further highlight the importance of awareness of climate disclosure mechanisms and carbon market functioning, as firms with higher levels of awareness exhibit a significantly greater propensity to engage in carbon offsetting. Taken together, the findings indicate that expanding voluntary carbon market participation requires policy and institutional designs that account for firm heterogeneity, strengthen organisational capacity, and foster positive internal attitudes towards offsetting, particularly among smaller and less engaged firms.