The diffusivities of oxygen in liquid Sn from 800 to 900 degrees C and in liquid Ba0.35Cu0.65 at 900 degrees C have been measured by a modified coulometric titration method using the galvanic cell : Q in liquid Sn or Ba0.35Cu0.65/yttria-stabilized zirconia/air, Pt. The diffusion coefficient of oxygen in Liquid Sn is independent of oxygen concentration and can be expressed as D-0(Sn) = 3.421 X 10(-3) exp (-33954/RT) with an activation energy of 33.95 kJ/g-atom (or 8.08 kcal/g-atom) which is in agreement with previous work. Strikingly, in the Ba0.35Cu0.65 liquid alloy, we have observed that the diffusivity of oxygen depends on oxygen concentration ranging from 2.95 X 10(-4) cm(2)/s for C-0 = 2.44 X 10(-3) atomic percent (a/o) to 8.62 X 10(-4) cm(2)/s for C-0 = 0.07 X 10(-3) a/o. The decrease in oxygen diffusivity with increasing oxygen concentration may be attributed to an enhanced configurational structural order in the Ba-Cu alloy melt due to the strong affinity between Ba and oxygen atoms.