The stalling behaviour of an Orenda CT-100, experimental, two-stage axial compressor was studied at the constant operating speed of 3000 r.p.m. Rotating stall was observed to commence at a mass flow coefficient of 0.435 and as the mass flow was reduced several different patterns of rotating stall were observed. In two ranges of operation "steady" patterns consisting or three rotating stalls were observed, in two other ranges of operation rotating stall was observed but the stall patterns were continually changing, while for very low mass flow operation the flow over the whole of the annulus appeared to be stalled. Reversed flow within the stalls was found to be an important feature of rotating stall.