To recover high pressure energy in a letdown station, a high pressure single screw expander (HPSSE) with 117 mm diameter is developed in our laboratory recently. This study presents the results of an experimental survey on the performance of HPSSE under varied inlet pressure and rotational speed. The inlet pressure of HPSSE ranges from 1.0 MPa to 5.0 MPa and the rotational speed is from 1500 rpm to 3000 rpm. The experimental results show that when the inlet pressure is 5.0 MPa, the maximum power output, volumetric efficiency, isentropic efficiency and shaft efficiency of HPSSE are 56.55 kW, 80.57%, 62.55% and 50.96%, respectively. The volumetric efficiency is immensely affected by inlet pressure under fairly slow rotational speed and a slight change in volumetric efficiency is observed under considerably high rotational speed. A high rotational speed is an effective method to reduce leakage in large pressure difference working conditions. (C) 2018 Elsevier Ltd. All rights reserved.