Purpose: This paper aims to propose a new blockchain system design to improve engineering, procurement and construction (EPC) companies’ supply chain for constructing oil and gas infrastructure, by mitigating cost and time inefficiencies. Design/methodology/approach: A case study analyses the supply chain of a sample EPC company. First, a literature review is conducted to explore the subject in academic literature. Second, information flows are mapped using responsible, accountable, consulted and informed analysis and cross-functional process mapping. Third, inefficiencies are identified. Fourth, the root causes of the inefficiencies are pinpointed using fishbone and five-times-why analysis. Fifth, a comparison is made between the linear and the blockchain information system via force-field analysis. Sixth, a specific blockchain system design is identified based on three external expert interviews. Finally, the new system is designed and a cost-benefit analysis is conducted. Findings: Major cost and time inefficiencies in oil and gas infrastructure developments are caused by a poor information flow in the supply chain. The new blockchain system design is a feasible solution, reducing cost inefficiencies by 12.4% and operation lead-times by 36.5%. Research limitations/implications: The confidentiality of the sample EPC company’s information represents a limitation. Originality/value: The research introduces a new blockchain system design, reducing cost and time inefficiencies in the project-development supply chain, including implementation processes.@en