NOVELTY - The unit has a floating component (34) provided with a sufficient buoyancy to float on water waves, and a piston assembly with a piston shaft and a hollow piston head (28) attached to the shaft. A piston reservoir (68) includes a volume that contains enough fluid at or above an output pressure so that the fluid is discharged from the unit during both compression and expansion strokes of the assembly. The buoyancy of a gas supply tube (50) is increased to cause a reservoir platform to rise to a surface, and a discharge conduit (52) is located in the shaft.    USE - Used for compressing a pressurized fluid e.g. air and water, which is utilized to power a turbine to generate an electric power, in response to natural wave action on a body of water e.g. ocean in an ocean application.    ADVANTAGE - The piston reservoir has the volume that contains enough fluid at or above the output pressure so that the fluid is discharged from the pressurization unit during both compression and expansion strokes of the piston assembly, thus minimizing the constriction of the unit and transferring more gas to the unit, and hence enabling to smooth out the delivery of gas from the piston reservoir, and preventing the gas from being discharged in sharp high-pressure pulses during the compression stroke only. The buoyancy of the gas supply tube is increased to cause the platform to rise to the surface for maintenance and servicing. The discharge conduit is located in the piston shaft to avoid imbalance or drag caused by the conduits attached laterally to the pressurization unit.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are also included for the following:    (1) a wave energy accumulator system comprising multiple pressurization stages    (2) a method of compressing a fluid.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic sectioned view of a compression unit.    Piston (26)    Piston head (28)    Floating component (34)    Buoyant surface float (36)    Input gas collection chamber (42)    One-way valve (44)    Opening (48)    Gas supply tube (50)    Discharge conduit (52)    Branch tubes (62)    Piston reservoir (68)