Summary The bundle flowline involves packaging multiple flowlines, control, and injection lines within a single carrier pipe. A bundle is claimed to provide an effective means of insulating flowlines by use of low-cost materials; however, no rigorous heat transfer analysis of bundled flowline systems has been offered by the literature or the vendors. For this reason, the thermal performance of bundle- insulated flowlines has been studied with a general-purpose, finite- element, partial-differential equation solver. Steady-state and transient cooldown performance were analyzed for six different bundle configurations. Overall heat transfer coefficients for individual flowlines within a bundle have been determined in addition to cooldown performance for different insulation levels and pipe sizes. These results have been compared with results obtained for the simple bundle geometry of a pipe-in-pipe system, and found comparable. To expedite the calculation of overall heat transfer coefficients for bundle flowlines, simplified heat transfer calculations were developed as an approximation to the finite-element solutions. These approximations are on the average within 5% of the finite- element solution.