What does it take for large-scale CCS projects to reach final investment decision? Evidence from Porthos in the Netherlands

• Stable climate policy and public ownership reduced risk for industrial for CCS projects. • Active state support and legal adaptation helped maintain momentum to investment decision. • Small, state-led partnerships enabled coordination in complex infrastructure projects. • Learning from failed projects created foundations for later carbon storage success. The Porthos project in the port of Rotterdam (Netherlands) is the EU’s first large-scale CO₂ transport and offshore storage system to reach Final Investment Decision (FID), marking a major step toward industrial decarbonization in the EU. Earlier Dutch CCS initiatives, including Barendrecht and the ROAD project, were cancelled or stalled, highlighting persistent challenges related to permitting, public acceptance, policy uncertainty, and business-case formation. This paper provides an empirical analysis of the enabling conditions that allowed Porthos to progress where earlier projects failed. The results show that four factors were decisive for advancing the project. First, a robust climate-policy framework reduced commercial and regulatory uncertainty. Second, a lean governance structure involving state-owned infrastructure firms and a limited group of industrial emitters enabled efficient coordination. Third, early identification of permitting and regulatory constraints, including the Dutch nitrogen ruling, allowed targeted government intervention to sustain project momentum. Fourth, the project benefited from cross-project learning from earlier Dutch CCS efforts, which provided technical knowledge, regulatory templates, and stakeholder-engagement experience, forming what we term project scaffolding . These findings offer practical insights for policymakers, regulators, and project developers seeking to design and support large scale CO₂ transport and storage infrastructure in Europe and beyond.