A scroll compressor is provided with a non-circular back pressure chamber which is still concentric about a center axis of the compressor, such as the center axis of the drive shaft. Stated another way, an inner seal and an outer seal define a back pressure chamber. The two seals are concentric, but at least one of the seals is non-circular. In this way, reduced a back pressure chamber can be provided while still allowing the amount of orbital movement necessary for the tap for communicating a compressed refrigerant to the back pressure chamber.