This paper discusses experimental and theoretical investigations about a re-designed co-rotation scroll machine, operating in compressor and expander mode. The machine has been tested under various operational conditions, with the aim to determine the influence of the input variables on the machine performance. A maximum internal isothermal efficiency in compressor mode of 53% was obtained, while an improvement of the internal isothermal efficiency in expander mode from 34% to 84% was achieved. In expander mode, a maximum internal shaft power of 4600 W was measured at a rotor speed of 41.6 Hz with a supply pressure of 6 bar. However, the mechanical losses reduce the net shaft power to 2.400 W. A deterministic model of the co-rotating machine in compressor and expander mode has been developed in order to understand the internal phenomena governing the machine performance. Using this model as an expander, the mechanical power, mass flow rates and exhaust temperatures were predicted within a range of ± 9%, ± 7%, and ± 10 K respectively, compared to experimental data. Further, the evolution of the deterministic and semi-empirical leakage areas are compared concluding that they are in the same order of magnitude, independently of the operation mode and operational conditions.