Isotopic compositions ( delta^18O and deltaD) and salinity (S) of 683 surface water samples from the Arabian Sea (AS) collected during 2008–2010, were measured to understand the factors controlling the spatio-temporal distribution of these parameters. From the distributions of delta^18O and salinity (S), and the relationships between delta^18O– deltaD and delta^18O–S, the following inferences have been drawn: (1) there is a broad correspondence between the geographic distributions of the delta^18O and S; (2) in spite of a large scatter, a statistically significant delta^18O–S relationship can be identified in much of the investigated part of the AS; (3) the delta^18O– deltaD regression line for all samples clumped together has a slope of 3.2 (± 0.16), much lower than that (7.37) for the global ocean surface water line (GOSWL), which in the case of the AS is seen only for samples with salinity < 34; (4) the linear relationship between delta^18O and deltaD breaks down completely in the months of March–May; (5) contrary to the adjoining Bay of Bengal (BOB), both delta^18O and S progressively increase from the equator northwards; (6) the delta^18O– deltaD and the delta^18O–d-excess relationships indicate strong kinetic fractionation due to evaporation from surface waters of the AS throughout the year, with enhancement during summer months.