To determine efficiencies of wellbore pressure control valves, results of manufacturer tests performed by a manufacturer of a pressure control valve (PCV) are identified. The PCV is configured to control flowrate of a fluid through a pipeline. The manufacturer tests correlate quantities of the fluid that the PCV allows to flow through the pipeline at respective open positions of the PCV. After installing the PCV in a flowline downstream of a production tree disposed within a hydrocarbon gas production wellbore to control hydrocarbon gas flowrate through the production wellbore, operational tests are performed on the PCV to measure quantities of the hydrocarbon gas that the PCV allows to flow through the flowline at the respective open positions of the PCV. The results of the manufacturer tests are compared with results of the operational tests. Based on a result of the comparing, an operational condition of the PCV is determined.