A unique turbine-driven hydraulic submersible pump (HSP) was installed successfully in a multiphase oil well in the North Sea Captain development. The purpose of the trial was to prove the field performance of the pump on high gas/oil ratio (GOR) flows before its wider deployment in the second phase of Captain field development. The full-length paper describes the pump concept and application specifics. The new HSP design has proved to be capable of extended operation on both single-phase and multiphase heavy oil and has operated successfully under transient downhole pumping conditions.