Abstract: In an impeller for a fluid energy machine with a hub and a plurality of rotor blades which are mounted on the hub and around which a medium may flow through the fluid energy machine and which form a blade duct between two neighboring rotor blades with a blade duct length which extends in the axial direction of the impeller, wherein each rotor blade is connected to the hub via a first transition region with a first curvature and via a second transition region with a second curvature and with a straight conical blade duct bottom of the blade duct formed between the first transition region and the second transition region.