In this study, a new cost model is developed for CO₂ pipeline transport, which starts with the physical properties of CO₂ transport and includes different kinds of steel grades and up-to-date material and construction costs. This pipeline cost model is used for a new developed tool to determine the configuration leading to the lowest levelized costs for CO₂ transport, for point-to-point pipelines as well as for simple networks on different types of terrain and for different time frames. The model optimizes inlet pressure, diameter, steel grade and number of pumping stations. Results show that gaseous CO₂ transport can give lower levelized costs than liquid CO₂ transport for point-to-point pipelines and for simple networks, if the CO₂ is stored in a reservoir with a low required injection pressure, like depleted natural gas fields. However, for storage fields with a required injection pressure of 8MPa or higher (like aquifers), CO₂ can be better transported in a liquid form. For onshore pipelines transporting liquid CO₂, the optimal inlet pressure is 9-13MPa and pumping stations are installed roughly every 50-100km. For offshore pipelines, pumping stations are not an option and the inlet pressure is determined by the length of the pipeline. The maximum inlet pressure is about 25MPa and for even longer pipelines, a larger diameter is selected. The levelized costs (excluding initial compression) for transporting 100kg/s (about 3Mt/y) over 100km are between 1.8 and 3.3€/t for liquid and 4.0-6.4€/t for gaseous CO₂ transport. For larger mass flows the costs are decreasing, for instance transporting 200kg/s (about 6Mt/y) over 100km are 1.2-1.8€/t for liquid and 3.0-3.8€/t for gaseous CO₂ transport.Furthermore, results show that higher steel grades lead to lower investment costs for onshore pipelines transporting liquid CO₂. Using X120 in the long term reduces the pipeline costs up to 17%. For gaseous CO₂ transport, lower steel grades (like X42 and X52) are the best option. Also offshore pipelines do not benefit from the development of higher steel grades over time because the thickness should be at least 2.5% of the outer diameter. The results indicate that oversizing the pipeline, to transport CO₂ from an additional source that is coming available later, is not always cost-attractive. This strongly depends on the time span of which further CO₂ sources are available and on the mass flows. Oversizing appears earlier cost-attractive compared to two point-to-point pipelines if the source with the largest mass flow becomes available first.