Flow measurements during deep stalled operation of an isolated compressor rotor of hub/tip ratio of 0.66 were carried out. It has been observed that during stalled operation the flow in the unstalled portion of the annulus operates at steady operating conditions corresponding to the point at which the blade row operates on recovery from rotating stall. From the static pressure measurement downstream from the rotor row it is evident that the static pressure in the stall cell is less than that in the unstalled region. The pressure deficit depends on the mass blockage in the case of single cell (low blockage) operation but has almost a fixed value during multi cell (large blockage) operation. In the present study, an improved stall model has been presented based on the observations in which the compressor characteristics during multi cell and single cell operations are separately determined. It has been found that critical blockage value per cell was of the order of 6 to 9 percent for the present rotor.