Various theories on the occurrence of the salinity minimum in the Arabian Sea are briefly reviewed. A special case of transformation by mixing of three water types, two of which have the same density but different temperatures and salinities, is discussed. It is shown that the salinity minimum of the Antarctic Intermediate Water 'moves' progressively to higher steric levels when this water mass mixes with the Red Sea, the Persian Gulf and the Arabian Sea High Salinity Water masses. The model suggests that the Antarctic Intermediate Water penetrates into the northern regions of the Arabian Sea. The peculiarities in the vertical temperature salinity structure at a few stations in the Arabian Sea are related to the mixing modes