To study the growth mechanism in growing superconducting thin films by the liquid‐gas‐solidification process, oxygen diffusivities in liquid Tl1Ba2Ca2Cu3and Ag1Tl1Ba2Ca2Cu3precursor alloys were measured by a modified coulometric titration method. The diffusivities of oxygen are very high of the order of 10−4to 10−3cm2/s. The logarithm of oxygen diffusivities is found to be reciprocally proportional to the logarithm of oxygen concentrations. This concentration‐dependent oxygen diffusivity phenomenon has not been observed in many metallic liquids investigated previously. An interstitial diffusion mechanism may contribute to the fast oxygen diffusion. The strong bonds between Ba and O atoms are proposed to enhance the configurational structural order and hence to quicken the oxygen diffusion that varies the oxygen concentration in Tl1Ba2Ca2Cu3and Ag1Tl1Ba2Ca2Cu3superconductor precursor liquids. ©1995 American Institute of Physics.