The performance of a multistage electrical submersible twin-screw pump (ESTSP) was evaluated under different operating conditions. The effect of working fluid, differential pressure, gas volumetric fraction (GVF), and pump rotating speed on the behavior of the ESTSP has been studied. Mineral oil and water were selected as test liquids. The pump was tested with a maximum differential pressure of 1000 psig. The GVF varies from 0% to 85%. The flow rate capacity and the volumetric efficiency were investigated in this research. An existing model to predict leakage flow of the single stage twin-screw pump is improved by extending the application for the multistage pumps. The model shows good agreement with experimental data under various operating conditions.