To even out seasonal variations in demand by gas consumers, gas that is not required is stored and then taken from gas storage facilities at times of peak demand. On storage, the gas that is not required is withdrawn from the pipeline and compressed to storage pressure. If the storage pressure falls below the pipeline pressure, the compressors are needed to increase it. The necessary capacity and transportation flexibility in operation of the storage facility is guaranteed by operating complete machinery trains or two process stages in a compressor casing in series and in parallel.