A surge control system for a compressor comprising a bypass passage controlled by a bypass valve to return flow to the compressor inlet for avoiding surge in the compressor. The bypass valve is controlled through a sensing of a compressor speed and flow. The compressor speed and the square root of the flow signal, which is proportional to the actual flow, are presented as a ratio for comparison with an empirically established constant. When the conditions of the compressor system are such that the ratio approaches the constant, the bypass valve is opened and the compressor experiences increased flow therethrough.