AbstractWide deployment of carbon capture and storage (CCS) will require extensive transportation infrastructure, quite often in the form of pipelines. The rollout of such large-scale infrastructure would undoubtedly require very large investments. In regions with several CO2 emission sources, it is possible that not all of the major CO2 sources will implement CCS at the same time. Shared oversized pipeline designs are often proposed in order to form a “cluster” of CO2 sources and serve as the backbone for an expanding CO2 transportation infrastructure, to which emission sources will be connected. This paper analyses the economics of using oversized and parallel pipelines for different typical pipeline length and CO2 flow rate combinations. For new CCS projects, the expansion methodology presented in this paper can identify the optimal pipeline design that minimises the cost per tonne of CO2 avoided over the life of the project. For existing projects, the expansion methodology identifies the optimal pipeline design change, which may include either using an existing pipeline as CO2 supply increases or duplicating pipelines.