In deep-ocean sequestration of CO2, it is difficult technically and costly to transport the CO2 with the use of pipelines on the sea floor, especially when the disposal site is deep and far from land. A promising alternative is using a ship as CO2 carrier and a pipe suspended vertically from a floating base at the site. The mechanical strength of the pipe has been investigated with consideration of the static tension due to the weight of the pipe itself and buoyancy of additional floaters, as well as the dynamic tension due to wave-induced motion of the floating base. We found that a pipe length of 4,000m is a feasible extension of conventional techniques. A pipe longer than 6,000m requires development of innovative technologies that are not yet developed.