Fast reaction of hydrated electrons (e(aq)(-)) with oxygen has been used to determine the dissolution and diffusion of oxygen in water by monitoring the decay of e(aq)(-) at 700 nm. Hydrated electrons in the irradiated volume (7.5 cm below the surface) were generated by pulse radiolysis technique. Water was purged with high purity nitrogen to remove dissolved oxygen, and subsequently, the lifetime of the e(aq)(-) formed on pulse radiolysis was determined at various times after exposure to atmosphere. The lifetime of the e(aq)(-) measured in the irradiated volume was negligibly affected until similar to 60 min after the water was exposed to atmosphere. Then onward, the lifetime of e(aq)(-) decreased as a result of oxygen reaching the irradiated volume. In another set of experiments, reaction of methyl viologen radical cations (generated by the reaction of e(aq)(-) with methyl viologen) with oxygen (k = 4.3 x 10(8) dm(3) mol(-1) s(-1)) was investigated to find out how the dissolved oxygen escapes from oxygen-saturated solution to the atmosphere by observing the increase in the lifetime of methyl viologen radical cations. In 140 min, concentration of oxygen comes down to the value present in the ambient aerated solution.