[en] This paper presents the results of an experimental study carried out on a prototype of a hermetic scroll expander, integrated into a gas cycle test rig, whose working fluid is HFC-245fa. This system was designed to test only the performance of the expander. It is mainly made up of a scroll compressor, a scroll expander, a heat exchanger and a by-pass valve. The latter is used to adjust the pressure ratio imposed to the expander. The expander is originally a compressor designed for heat pump applications and characterized by a nominal power input of 2.5 kWe. Performance of the expander is evaluated in terms of isentropic effectiveness and filling factor as function of the main operating conditions. The study also investigates the impact of oil mass fraction on the expander performance. Maximum overall isentropic effectiveness of 71.03% is measured, which is partly explained by the good volumetric performance of the machine. Using the experimental data, parameters of a semi-empirical simulation model of the expander are identified. This model is used to analyze the measured performance of the expander. Finally, a polynomial empirical model of the expander is proposed for fast and robust simulations of ORC systems.