Abstract: The invention relates to a rotary displacement compressor having volume ratio regulation. A connection channel (8,9,10) connects the working space of the compressor to the pressure channel (5). In the channel (8,9,10) there is provided means (13) for sensing the direction of flow through the channel. The direction of flow is an indication of whether there is over or under compression. Signals from the flow direction sensing means (13) affect the position of a movable edge (29) of the outlet port (32) so that this edge (29) will move to a position where the internal compression complies with the outlet pressure. By using the direction of flow as the governing parameter for the volume ratio regulation instead of the pressure difference or the power consumption of the prime mover according to known technique, a more accurate adaption of the volume ratio to the outlet pressure is achieved.