This paper reports an experimental study of multistage axial compressor operation under reverse-flow conditions. The experiments were performed on a high hub-tip ratio, three-stage, low aspect ratio compressor. Unstalled and stalled performance characteristics are presented for two builds with different blade-stagger angles. A new finding is the demonstration of a flow-mode transition from large-scale asymmetry (rotating stall) to blade-to-blad e periodic ("annulus stall") at a low reverse-flow coefficient, with a consequent discontinuous drop in the pressure-rise characteristic. The annulus-stall flow regime was examined using high-response measurements of all three velocity components and pressure. These blade-passage-resolved measurements provide the first detailed kinematic picture of the flowfield structure that exists in multistage axial compressors during reverse-flow operation. The experimental results reveal that the flowfield is strongly three-dimensional and show close similarities between the structure of the reverse flow and the rotating-stall cell flowfields.