Technical and economical evaluation of pipeline transportation of hydrogen, natural gas and their mixtures is presented. Particular emphasis is placed on those aspects of pipeline design that bear a direct relevance to the final levelized cost of transmission. The conventionally held belief that hydrogen can only be transmitted over relatively short distances (because of its low volumetric energy content) is challenged by results indicating that under certain conditions (mainly high production pressures and large enough markets), it may be economically feasible to transport hydrogen or hydrogen-natural gas mixtures over long distances. Attention is also given to the option of transmitting hydrogen through existing natural gas pipeline networks. It is shown that inefficiencies introduced due to the use of existing systems can be overlooked because of the large reduction in transmission costs brought about by the potential to produce hydrogen at elevated pressures.