In processes and systems utilizing a compressor to fill a vessel with gas, for example, in the filling of the fuel tank of a vehicle that operates on compressed natural gas (CNG), a number of advantages are realized by establishing independent control over the flow rate of gas discharged from the compressor, such as on the basis of the compressor discharge pressure, utilizing feedback from one or more gas pressure sensors. In representative embodiments, a detected or actual measured compressor discharge pressure can serve as a process variable, in a feedback control loop for regulating the output of the compressor.