For extruders, energy consumption depends on the energy required by the drive motor and for heating and cooling of the extruder barrel. This work investigated the energy consumption of high speed twin and quad extruders. Both extruders had 15-mm-diameter screws with length-to-diameter ratios of 45:1 and the same 22-kW motors, but the different number of screws changed the clearance between the screws. Energy consumption was evaluated as a function of screw speed, feed rate, and polyethylene type and molecular weight. On-line measurements of viscosity were correlated with the mechanical and thermal energy consumed by the extruders. Results are discussed with respect to material structure and viscosity as well as extruder design.