A hybrid gas compressor has at least one rotor and shroud which define a compressor gas path extending from an inlet to an outlet. The compressor includes at least two compression stages and one diffusion stage between the inlet and outlet, the compression stages including respective circumferential arrays of blades extending from the rotor and the diffusion stage including a circumferential array of vanes between the compression stages. Blade aerodynamic loadings may be controlled, particularly in the last stage, to provide desired compression characteristics across the compressor. A bleed outlet is optionally located between the inlet and outlet for bleeding from the gas path.