A basic approach to the application of gas compressors is presented to explain the effect of clearance in a reciprocating compressor cylinder. Compression efficiency is not affected by clearance volume, because most of the work required to compress the gas in the clearance volume is recovered when it expands back to suction conditions. Use of clearance enables the operator to maximize the horsepower in a unit by using larger cylinders. Purchase or lease of a well designed unit awards the operator with a broad range of operating conditions. This becomes cost effective. Otherwise, changing out units becomes expensive and time consuming to the producer.