The diffusion coefficient of O-2 in H2O and D2O has been determined as a function of temperature from -0.5 to 95 degrees C, using the Taylor dispersion technique with optical absorbance detection at 200 nm. Over this temperature range, significant deviation from both Arrhenius and Stokes-Einstein behavior is found. A practical interpolation formula for the H2O solvent is (T in Kelvin) log(10)[D/cm(2) s(-1)] = -4.410 + 773.8/T - (506.4/T)(2) and, for the D2O solvent, log(10)[D/cm(2) s(-1)] = -4.706 + 903.6/T - (526.6/T)(2). As a test of the apparatus, the diffusion coefficient of nitrobenzene in water was carefully measured and found to be 1.04 x 10(-5) cm(2) s(-1) at 26 degrees C and 2.14 x 10(-5) cm(2) s(-1) at 60.1 degrees C.