One conventional development of green field off-shore oil is by using local fixed platforms or floaters/FPSOs, oil processing and off-shore loading. These are costly and complex facilities to be installed and manned by expensive logistics with inherent safety challenges. In very remote areas, and/or hostile climatic/weather environments, local surface processing may not be considered acceptable on a range of parameters. In more developed, mature areas, subsea tie-back solutions to existing processing facilities are usually applied. The maximum tie-back distance to existing infra-structure is often limited by conventional concepts struggling with range limitation, and expensive complex solutions for pipeline heating, to provide acceptable flow assurance. The Thermoil™ concept aims to provide for full subsea development, of oil dominated fields, and facilitate long distance tie-back to a central processing facility or to an onshore oil terminal. It consists of ultra-long insulated pipe-in-pipe flow segments with subsea pumping and heating facilities which can expand into a flexible infrastructure serving multiple fields simultaneously or in sequence.