A method an apparatus for filling a vessel with compressed gas is disclosed. Gas is compressed into the vessel at a predetermined flow rate using a variable speed pump or compressor. The flow rate is adjusted to increase the gas pressure at a predetermined rate of change. The flow rate is adjusted based upon the instantaneous value of a measured parameter such as gas temperature or pressure or ambient temperature. The parameter is measured by a transducer and the value is fed back to a controller which adjusts the speed of the compressor or pump to produce the flow rate needed to achieve the predetermined pressure rate of change.