A hydraulic gas compressor has no moving parts and compresses gas at the expense of hydraulic energy by means of entrainment in a downward moving column of liquid with subsequent separation of gas and liquid at depth. Documentation is cited giving the history and performance data for large hydraulic air compressors built around 1900. An analysis is presented based on one-dimensional bulk parameter modeling of the flow, which enables computerized calculation of the performance of hydraulic gas compressors. The results of small-scale experiments are presented showing agreement with analytical results. It is further shown that the analytical results agree with reported performance data for old large-scale compressors. Unique capabilities of the compressor for transducing and transforming energy are described and application studies are suggested in several areas. Calculated results are presented as an example, for the design and performance of a large air compressor, showing the effect on performance of varying the applied hydraulic head.