Abstract: The outlet of a centrifugal compressor is provided with an annular row of movable diffuser vanes which align with the fluid flow direction to prevent a surge condition. Each movable diffuser vane has a pivot axis forward of the vane's center of pressure to cause the fluid from the impeller to move the vane such that the flow meets the diffuser vane leading edge with a near-zero incident angle. The vanes are floating or freely movable on the pivot axis except for spring bias which prevents flutter. In some embodiments, the movable vanes are upstream of primary fixed diffuser vanes, of the vane-island or of the airfoil vane type, and are movable between a closed position abutting the primary vanes to variable open positions which create auxiliary diffuser channels.