Abstract: A pressure profile versus flow rate is determined for a flow control system using positive displacement or a flow meter to measure flow. The profile is used as a pressure reference for closed loop pressure control of flow during the transient period following a change in commanded flow rate to reduce the time required to reach the new flow rate with compressible fluids and compliant output lines. Alternatively the pressure profile is automatically determined and updated continuously to adapt to environmental conditions affecting the accuracy of pressure controlled fluid flow.