Abstract: A tube bundle, suitable for the transportation of gas from a subsea wellhead, comprises (a) an insulated external casing, (b) an internal production line for gas, moisture and possibly oil or condensate and (c) an internal tube for carrying a heating medium through the bundle to its wellhead end. The heating tube has a tapered or stepped layer of insulating material with the insulation increasing in thickness in the direction away from the wellhead.The combination of heating and carefully designed insulation is particularly effective in preventing hydrate formation in the gas line.