The distributions of dissolved oxygen content in the Arabian Sea during the southwest monsoon season, 1963 are presented through vertical sections and horizontal charts. The surface oxyty variations are considerable and these have been attributed to large variations of surface temperature and salinity, circulation, photosynthesis, etc. The surface waters are found to be supersaturated with oxygen throughout the Arabian Sea, except in regions of intense upwelling. The oxyty in the surface layer is nearly uniform, indicating effective mixing in this layer. Below the surface layer, a strong oxycline (layer in which oxygen decreases with depth) which coinci des with the thermocline has been observed. The oxypleths in the oxycline tended to rise towards the Indian coast. The oxygen minimum intermediate layer could only be observed clearly in the northern Arabian Sea. Across the Gulf of Aden and in the southern latitudes, subsurface oxygen maxima at different steric levels are found. The studies revealed that these oxygen maxima are due to the transport of oxygen rich Subtropical Subsurface Waters across the equator. The high oxyty of the deep waters has been attributed to the penetration of the water mass originating in circumpolar regions.